How to Clean AC Evaporator Coils – Part 2

By |Last updated on |Central AC Maintenance|208 Comments

How to Clean AC Evaporator Coils – evaporator coil inspection and cleaning with no-rinse spray foam coil cleaner. This project is continued from How to Clean AC Evaporator Coils – Part 1.

Table of Contents

  1. How to Clean AC Evaporator Coils
    Seasonal exterior coil surface cleaning with a spray-on foam.
  2. How to Clean AC Evaporator Coils – Part 2 (this project)
  3. Heavy Duty AC Evaporator Coil Cleaning
    Deep cleaning with professional coil cleaner, pump sprayer and brush.
  4. How to Clean Inside of AC Evaporator Coils
    Interior coil cleaning by removing the coil end plate, best for very dirty coils.
  5. AC Evaporator Coil Cleaning with Pump Sprayer and Brush
    Clean the coils inside and out.
  6. How to Install a Honeywell Ultraviolet Light Treatment System
    Prevent mold and algae with a disinfectant UV germicidal light.
  7. How to Install a Honeywell Ultraviolet Light Treatment System – Part 2
  8. How to Clean and Straighten AC Condenser Coils
    Outdoor compressor unit maintenance.

AC Evaporator Coil Inspection

The following is a photo of my central air conditioner evaporator coils before cleaning. The AC coils look very clean already because I service my system regularly. Of some concern is the rust on the ends of the frame. The unit is about 9 years old and rust is common in these areas. The greenish/whitish discoloration on the copper refrigerant lines is from dissolved copper deposits that have dried. The plastic drain pan looks in good condition with no cracking or leaks. Overall, not too bad for a 9 year old evaporator coil. I should expect to replace the coil and/or air handler in a season or two as it approaches the end of its expected life.

Air Conditioner Evaporator Coils

Air Conditioner Evaporator Coils

Evaporator Coil Icing & Freezing

If your coils look clean but are freezing over, it may be caused by:

  • Clogged air filter.
    A clogged filter can restrict the air flow through the coils causing condensate water to freeze on the coils. Coils need a large volume of warm air flow to stay above freezing. This is a vicious cycle because the ice grows blocking more of the surface.
  • Clogged interior coils.
    The exterior coils may appear to be clean, but the interior surface can be dirty. The interior surface is on the upwind side (closest to the blower motor) where dust, dirt, pet hair, loose insulation and such will stick. See Heavy Duty AC Evaporator Coil Cleaning for how to inspect the interior side of the coils.
  • Refrigerant Leak
    AC systems can leak refrigerant through failing brazed joints, pin hole leaks cause by corrosion, bad gaskets, etc. resulting in a low refrigerant charge. A low charge will cause the temperature of the liquid refrigerant flashed to a gas through the expansion valve to be much colder than normal causing them to freeze. The gas is much colder because there’s not enough of it to fill the coils; the gas over-expands inside the coils, resulting in lower pressure & lower temperature, hence freezing. The Joule Thomson Effect (highly technical) describes the process.These N style evaporator coils are freezing over, starting at the bottom closest to the expansion valve. An HVAC tech found the coils to be about 2 lbs low on R-22 refrigerant:

    Freezing AC Evaporator Coils - Low Refrigerant Charge

    Freezing AC Evaporator Coils – Low Refrigerant Charge

    My AC coils in this project were slowly leaking, needing a recharge of about 1 lb of R-22 per season. They didn’t freeze but the system grew less efficient and the air blowing from the vents wasn’t as cold as it should be.

Air Conditioner Evaporator Coil Cleaner

I purchased a can of Frost King Air Conditioner foaming no-rinse coil cleaner from Home Depot:

Frost King - Foaming Air Conditioning Coil Cleaner

Frost King – Foaming Air Conditioning Coil Cleaner


The Frost King coil cleaner has been replaced by the Thermwell Products AC-Safe Air Conditioner Coil Foaming Cleaner. (Thermwell owns the Frost King brand.) The AC-Safe coil cleaner is non-flammable and won’t damage plastic condensate drain pans.

Nu-Calgon Evap Foam No-Rise Coil Cleaner

The Nu-Calgon Evap Foam no-rinse coil cleaner is specifically formulated for cleaning air handler evaporator coils and approved for use in and around food processing areas. It’s available from I like the Nu-Calgon Evap Foam because the manufacturer’s page (previous link) includes directions and literature. I used a similar Nu-Calgon coil cleaner in the Heavy Duty AC Evaporator Coil Cleaning project.

Clean the AC Evaporator Coils

The foaming coil cleaner is sprayed directly on the AC coils, coating the surfaces evenly and thoroughly. It’s best to do this on a warm day when the AC will be running to help rinse the coils with condensate water.

AC Evaporator Coil Cleaning with No Rinse Spray Foam

AC Evaporator Coil Cleaning with No Rinse Spray Foam

The spray foams nicely on the coils.

AC Evaporator Coil Cleaning: No Rinse Spray Foam

AC Evaporator Coil Cleaning: No Rinse Spray Foam

The no-rinse foam cleaner breaks down and liquifies quickly for a good rinsing action.

Evaporator Coil Cleaning: No Rinse Foam Breaks Down Quickly

Evaporator Coil Cleaning: No Rinse Foam Breaks Down Quickly

In minutes the foam is rinsing itself off and draining away. Always check the PVC drain line is free of algae and unclogged. I poured a quart of 50/50 solution of household bleach and water in the drain pan to keep the line clear. You can also buy time-release algae tablets to drop in the drain pan.

AC Evaporator Coil Cleaning: Plastic Drip Pan and Drain Line

AC Evaporator Coil Cleaning: Plastic Drip Pan and Drain Line

The evaporator coil access panel is reattached with the sheet metal screws. The top and bottom seams are then sealed with HVAC metal foil tape:

Reattach the Evaporator Coil Access Panel and Seal with Metal Tape

Reattach the Evaporator Coil Access Panel and Seal with Metal Tape

Take care not to tape over the manufacturer’s label on the access panel because the service technician may need this data:

Air Conditioner Evaporator Coil Access Panel Sealed with HVAC Tape

Air Conditioner Evaporator Coil Access Panel Sealed with HVAC Tape

The attic AC air handler is now ready for another hot summer of cooling. The last task is to turn on the thermostat.

Attic Air Handler - Ready for Summer

Attic Air Handler – Ready for Summer

HVAC Air Handler Basics

Now you’re familiar with the basic components of the attic air handler and the importance of changing the air filter and performing routine system maintenance. If your AC system needs professional servicing, you’ll know what the HVAC technician is talking about. Annual Service Contracts are available from HVAC companies and usually cost less than the sum of ad-hoc maintenance calls.

Heavy Duty AC Evaporator Coil Cleaning

The Heavy Duty AC Evaporator Coil Cleaning tutorial explains how to inspect and perform a heavy duty cleaning which is best for cleaning really dirty coils:

AC Evaporator Coils - Interior Clogged with Dirt and Mold

AC Evaporator Coils – Interior Clogged with Dirt and Mold

AC Condenser Coil Cleaning

It’s equally important for the outdoor AC condenser coils (also called “compressor coils”) to be clean for proper air flow and heat exchange. The fins on my condenser coils were also badly bent. That project is explained in How to Clean and Straighten AC Condenser Coils.

Stay cool!
Bob Jackson

Copyright © 2019   Reproduction strictly prohibited.


  1. Albert July 6, 2009 at 4:44 pm - Reply

    thanks for the great educational site and great pictures

  2. Blade August 4, 2009 at 11:56 pm - Reply

    Does this also clean inside coils. My outside one like the one in your picture looks clean however using a mirror and flashlight I saw that the inner part is really dusty and the AC Tech guy said it would be about $200 to get the Coil out and clean it

  3. Bob Jackson August 5, 2009 at 7:20 am - Reply

    It’s depends on how dirty the inside surface of the coils are. Regular cleaning will prevent buildup on both surfaces.

    If you believe the inside of the coils need particular attention try an acid-based cleaner and pump sprayer with a wand to apply the cleaning chemicals with a bit more force to loosen the dirt on the inside surface.

    Don’t spray too hard or the solution will shoot through the coils and rain down onto the heater and blower fan section if you have an updraft model like mine. You want the cleaning solution to wick down the coils and into the condensate pan.

    Pump sprayer:

    Acid-based cleaner: with the pump sprayer.

    A gallon of Cal-Brite will cost you about $30 and figure another $15 for the sprayer – call it $50 for supplies, plus your time and labor. You’ll need gloves and safety glasses, too. If the results are not satisfactory, you’ll be making that service call for a professional cleaning for $200, bringing the total cost to $250.

    If I were in your situation, I’d call the professional to give the coils a thorough cleaning inside and out – and – have the A/C tech check my duct work for leaks may be allowing dirt to get past the filter and onto the coils.

  4. Hoan August 20, 2009 at 12:49 pm - Reply

    Thanks for great write up. This is the only one that I searched that shows how to clean the ac evaporator coil (inside the house). Most others show how to clean the condense coil (outside of the house, I think) but since your write up is so detailed, I’d would love to see one from you if available.


  5. Hung Lam September 11, 2009 at 5:17 pm - Reply

    Thanks Bob, this is what I needed. I this article with a lot of details and pictures.

  6. Ernie November 2, 2009 at 4:38 pm - Reply

    I wasn’t to sure what spray to use on my indoor coils so this really helped out. Short, with important details and straight to the point.


  7. Tony November 27, 2009 at 7:57 pm - Reply

    I applied Nu Calgon foam self rinse cleaner today to my evap coil in the attic. I am not running a/c as outside temps are cool (high sixites). Will I need to rinse with a sprayer?

  8. Bob Jackson November 28, 2009 at 9:01 am - Reply

    The Nu-Calgon Evap Foam aerosol spray can is a “no rinse” product.

    It’s available from

  9. richard January 10, 2010 at 8:36 pm - Reply

    great article, my question now is that it is now winter time and i want to clean my inside heatpump coils like what is described in this article and since it is heat not cooling season should i rinse the coils off carefully with a pump up garden typ sprayer just enough that it will drain into the condesate pump tank. Also, is it a good idea to lightly spray a diluted mixture of water and chlorox to kill any mildew that may be there, let it set for a few minutes then rinse it off as well.

    • Bob Jackson January 11, 2010 at 7:20 pm - Reply

      The no-rinse coil cleaning products don’t need rinsing, but since it’s heating season you should shut off the heat until the foam breaks down and drains off the coils along with the dirt. The weak bleach and water rinse would hurry the rinsing action, but shouldn’t be needed with the coil cleaner as it disinfects. If in doubt, give it another shot of no-rinse coil cleaner.

      Should something be sticking to the coils, it can be oh-so-gently brushed away with a very soft bristle brush. The coil fins are very fragile and bend easily – go slowly and check your work.

      If you do use bleach and water, take care to spray lightly such that you don’t shoot through the coils and drip onto the gas burner and blower motor. The spray should always adhere to the coils and wick it’s way down to the condensate drain pan.

      For light mildew concerns – that is so light you can’t really see it but suspect something is always living in a moist environment – give the insulated cabinet walls a good shot of Lysol spray.

  10. richard January 11, 2010 at 8:23 pm - Reply

    thanks for quick reply, great site.
    My heat pump is a trane unit. Going to clean mine this weekend like what you described in your article. Once i spray everything good with the lysol should i let the unit stay off for a while? I plan on cleaning the coils twice and vacumming out the insulated cabinet walls the best i can, i have duck board instead of metal.

    • Bob Jackson January 12, 2010 at 5:23 am - Reply

      > Once i spray everything good with the lysol should i let the unit stay off for a while?
      You don’t have to wait for the Lysol to dry. It does the job on contact.

      Not sure about vacuuming the cabinet walls, use a brush attachment so it doesn’t grab and pull the insulation off the duct board.

  11. mike June 14, 2010 at 6:49 pm - Reply

    how often should I change the main filter ??

    • Bob Jackson June 15, 2010 at 4:43 am - Reply

      Change your A/C filter at least monthly during the heating or cooling season. More often if you notice the filter is dirty. A dirty filter obstructs the airflow, lowers efficiency and raises your cooling or heating bill.

      A good digital thermostat will have a “Change Filter” reminder to change the filter after the 10 running days, which equates to 240 hours of operation. I use Honeywell Digital Touchscreen thermostats with programmable schedules in my home. See the VisionPRO 8000 7-Day Programmable Thermostat.

  12. al June 17, 2010 at 4:04 pm - Reply

    Just had HVAC tech out for recent leak into ceiling. He said coil was not installed level,is now rusted, and requires replacing along with plenum. Is it possible to repair/clean coil instead? Also recommended replacing outside condenser unit to correspond with new coils on the market. Is it possible to find the older model coil? Unit is ~11 years old.

    • Bob Jackson June 17, 2010 at 5:34 pm - Reply

      Which part is rusted? The coil fins and refrigerant tubes? Or only the end plates of the A frame? Is the rust cosmetic or is the structural integrity of the A frame threatened? Are the coils leaking refrigerant?

      Cosmetic rust can be ignored, but will eventually become a problem. Really dirty coils usually can be cleaned, though it will take more than a casual cleaning with an aerosol spray, requiring a pump sprayer, brushes and special coil detergent by a pro.

      The HVAC tech is giving you good advice: If the evaporator coil is being replaced, why not go with current products that are more efficient? The evaporator coil is matched to the condenser unit and is the reason for replacing both.

      I would think you can get a direct replacement for your old coil. A few phone calls with the make, model and serial # of your air handler should answer.

  13. jean June 23, 2010 at 2:49 pm - Reply

    how often do you need to replace a coil and how expensive? Sometimes it gets frozen up?

    • Bob Jackson June 23, 2010 at 7:25 pm - Reply

      An average evaporator coil should last maybe 10 years or longer if the system is well maintained. The parts cost for a replacement coil will vary with the brand and size (tonnage) of the A/C system; usually in the range of $300 for a 2.5 ton A frame to $750 for a 5 ton unit. Labor to drain the refrigerant, remove the old coil, install the new unit and recharge the refrigerant will be extra – several hundred dollars.

      > Sometimes it gets frozen up?

      I’ve fortunately not had this happen to me. For advice see Troubleshooting a FROZEN Evaporator Coil at HVAC Parts Outlet.

  14. Jim McCann June 29, 2010 at 3:09 pm - Reply

    The A Frame in my unit is aluminum. It is 10 years old and looks to be in great shape. It is however freezing up and the tech tells me that there is sludge clogged inside the coils and the entire A frame must be replaced. He said he tried to blow it out and pushed 200 psi through. He also said they need to install an inline dryer and filter. This is going to get real expensive but he says it is all he can do as he cannot get the unit above 31 degrees and it will just freeze up again.

    • Bob Jackson June 29, 2010 at 4:55 pm - Reply

      The sludge in the coils is obstructing the warm air intake, causing the condensation on the coils to freeze due to insufficient air flow and heat exchange. Ask the HVAC tech a combination of soaking in a chemical wash, light brushing and air will get the coil clean enough to prevent freezing. It’s a trade off between cleaning labor and replacement cost.

      If you open the front of the air handler, you can see how bad the sludge is by shining a flashlight inside the A-frame and looking down through the fins with a hand mirror held on the other side.

  15. Jim McCann June 30, 2010 at 11:34 am - Reply

    They are telling me the sludge is inside of the tubing not on the outside. I thought it was a closed environment and do not see how sludge can get into the freon to cause a blockage.

  16. Liviu July 13, 2010 at 5:44 pm - Reply

    Hi guys, anybody knows how to clean a sealed A frame evaporator? Mine does not have any access holes so I was thinking to cut open a panel and after cleanning screw it back together and use a metal tape to seal it. The problem is my unit does not have much flow. The top part of the A frame I could see, but does not seem to be very dirty. I can not see the bottom side. Any ideeas?

    • Bob Jackson July 13, 2010 at 6:31 pm - Reply

      It would help to see photos of the front, back and sides of your air handler unit to be sure there isn’t an access panel.

      If there isn’t an access panel, you could cut a 5 inch square access panel on the left and right sides in the plenum (rigid ductwork) above the coils to inspect with a flashlight and spray the foaming coil cleaner. The method is the same as cutting a hole for the take-off starting collar in this project: – see about midway down the page for the work with a utility knife. When you’re done, apply metal foil HVAC tape the panel cutouts first with the 1/2 width of the tape exposed along the sides – it’ll look like a big bandaid – then reinsert the panel and seal tape against the plenum ductwork. Smooth down the foil tape to ensure there are no air leaks.

  17. Liviu July 13, 2010 at 7:06 pm - Reply

    Hi Bob, thanks for the info. I have a hole in the back of the unit where the 6 in duct from the humidifier unit goes in and I think I can squize my hand in there but I was afraid all the goo and stuff from the A frame will go into the blower at the bottom and short everything. The whole unit looks like it was built like a Rolls Royce: “No problems for life”. I wished. What if I cut a 12in x 12in hole to access the A frame?

    • Bob Jackson July 14, 2010 at 7:25 am - Reply

      > I have a hole in the back of the unit where the 6 in duct from the humidifier unit goes in…

      That could work, but if there’s a starting collar you wouldn’t be able to see what you’re doing or inspect the condition of the coils.

      > I was afraid all the goo and stuff from the A frame will go into the blower at the bottom and short everything.

      The foaming aerosol coil cleaner is designed to adhere to the coils, break down over several minutes and run down the coils into the condensate drain pan, washing away the dirt. There shouldn’t any drips on to the blower fan or motor when applied per the manufacturer’s instructions.

      > What if I cut a 12in x 12in hole to access the A frame?

      I don’t recommend such a large cutout in the plenum if held only with metal foil tape. There’s a fair amount of air pressure in the plenum when the system is running and I wouldn’t trust metal foil tape to withstand the pressure over time, risking a break in the seal and/or panel blowout. Hence the reason for two small field expedient 5″x5″ access panels – large enough to see what you’re doing, but small enough the total surface area and air pressure should be OK for metal foil tape. Be sure to dust off the plenum so the tape seals well.

      If you’re set on installing a large duct access panel in the plenum, or want a professional looking job, Lau Industries and Kees make duct access panels. These are insulated duct access doors with a gasket to seal against the plenum and metal tabs (similar to a starting collar) that grip the inside of the plenum to prevent blowouts.

  18. Eric July 20, 2010 at 12:36 pm - Reply

    My evaporator in the crawl space is leaking. I opened it up and it has a lot of rust on the bottom tray. Everything else is in good shape. The leaking condensate collects under the unit. Should I just install a second pan and drain to the exterior?

    • Bob Jackson July 20, 2010 at 6:24 pm - Reply

      If you can replace the rusted condensate pan with a new plastic pan, that’d be the way to go. It’s worth a service call from an HVAC tech to get an estimate.

      > Should I just install a second pan and drain to the exterior?
      Not exactly sure where you intend to place the second pan. If you mean immediately underneath the rusty evaporator coil condensate pan, I doubt it would work because water will wick along the sides of the rusty pan, dribble off to the side and miss the new pan wetting the insulated walls causing mold/mildew.

      Post back with what you decide to do.


  19. Joe L. July 30, 2010 at 8:58 pm - Reply

    Hello Bob:

    Thank you for all the information. You are very kind to respond to so many people.

  20. J.D. August 5, 2010 at 1:58 pm - Reply

    I took the cover off my evaporator, its not an A-frame but slanted. The previous home owners obviously didn’t change filters as dust was completely covering fins on intake side of evap. Took a vacuum and soft brush and got the top layer off, I am assuming there is a lot still trapped between the fins as air flow still seems very restricted. Would the Frost king sprayed into the outtake side push the dust out? I have to try something as in this 105 degree weather, we can only get to 90 degrees and the air is just barely blowing out of the vents. Thanks for this informative site.

    • Bob Jackson August 5, 2010 at 4:54 pm - Reply

      Shine a flashlight through the fins onto a hand mirror to inspect how badly the fins are clogged.

      Buy a new garden pump sprayer with a spray wand, fill it with warm water, adjust the spray nozzle to a slightly open pattern. Turn off the A/C system. Place a plastic pan under the coils to keep the blower motor dry and catch the water. Spray the coils to knock out the dirt that’s between the fins. Spray gently (this isn’t a pressure washing) so as not to bend the fins, which would further block the airflow. Spray on the coil cleaner and let it do its work. Rinse with the pump sprayer and reinspect with the flashlight and mirror. Repeat if necessary.

      I say “buy a new pump sprayer” because you definitely don’t want to reuse a garden sprayer that’s had chemicals in it.

  21. Wiley Richards September 16, 2010 at 7:26 pm - Reply

    I’ve noticed my walls with what appears to be mold. I recently discovered that by evaporator coil was full of dust. I have a York 2 ton dual system. The unit has been working well over the past 2 weeks since cleaning the coil. We are thinking of changing the furance to allow for the filter to set properly. Is their any reason to replace the evaporator? Has anyone else found mold in their home from a clogged evaporator?

    • Bob Jackson September 16, 2010 at 7:50 pm - Reply

      Do you have one of those combination thermometer and humidity tabletop sensors in your home? A decent one costs $30 to $40. The indoor humidity must have been really high because the clogged evaporator coils couldn’t remove water from air through condensation on the cold coils. 40% to 60% relative indoor humidity is considered to be comfortable and normal if the A/C is working properly.

      > We are thinking of changing the furance to allow for the filter to set properly.
      > Is their any reason to replace the evaporator?
      I take your meaning to be there are large gaps that allowed air & dust to bypass the filter and clog up the coils. Once you’ve corrected the filter problem, the evaporator coils should be fine if clean, there are no refrigerant leaks and the fins are straight.

  22. Wiley Richards September 17, 2010 at 3:31 pm - Reply

    My HVAC was installed in 1997, at the time my home was built.I currently have a leak in my Coil, being that I added freon on Sept. 6 and my system required 1/2 pound today.

    I have a friend that performs HVAC work on the side. He quote $3,200.00 to install a 3 ton 410 Unit. What would you consider to be the downside in having an experienced(30 years)person who does this work on the sider verus a service company who has quoted me to do the same work for $6,800.00 to $8,300.00

    • Bob Jackson September 17, 2010 at 5:26 pm - Reply

      Hey! I might need your friend to do a job for me next spring!

      Here’s what I’d do:
      1) Check your friend’s references on recent jobs to make sure his other customer’s are happy.
      2) Structure the deal such that your friend won’t get paid until you have a licensed HVAC company
      inspect and approve the work.
      3) Put the terms and payment criteria in writing.

      Tell the 3rd party HVAC company that it’s a newly installed system and you wanted a 2nd opinion everything is as it should be.

  23. Wiley Richards September 17, 2010 at 7:16 pm - Reply


    My friend’s costs does not cover new ductwork. My home is 13 years old and I believe several of my rooms have mold from a leak of my evaporator coil. What are the chances my duct work can be cleaned?

    • Bob Jackson September 18, 2010 at 9:04 am - Reply

      I’ve no experience with duct cleaning. Is your duct work exposed in some places where you could open it up for inspection?

  24. Wiley Richards September 18, 2010 at 11:14 am - Reply

    You can view it only if you remove the coil from the closet.

  25. Wiley Richards September 19, 2010 at 6:01 am - Reply


    I would ask, do you think I should have the duct work cleaned before replacing my unit? My friend suggests I replace my unit first. While a local radio “Fix it Up” show suggest duct work cleanig first.

    • Bob Jackson September 19, 2010 at 8:11 am - Reply

      The advice I received from the Trane dealer when I replaced my system in Florida was:

      1. Remove the old air handler.
      2. Have the ducts cleaned while there’s unobstructed access to the main
      plenum and trunk lines.
      3. Install the new air handler.

      Unfortunately, the duct cleaning crew failed to show up that day and I refused to let them do it afterwards because I saw no obvious issues with the ducts and I felt it was an optional “plus” service.

      BTW – when I change my air filter, I turn on the system fan and give the air intake a 15 second shot of Lysol spray to circulate disinfectant through the system.

  26. Richard huang December 2, 2010 at 3:40 pm - Reply

    Great information!I have 10 years old evaporator coil and steal pan ,the Air condition is located on 2nd floor close.
    Q1: Can I replace the whole evaporator and pan?
    Q2: Do you think there is possible to find simliar unit to replace it all at this type old model?
    Thank you

    • Bob Jackson December 2, 2010 at 5:49 pm - Reply

      > Q1: Can I replace the whole evaporator and pan?
      A rusted through condensate pan can usually be replaced separately from the coils, and the evaporator coil can be replaced as well.

      > Q2: Do you think there is possible to find simliar unit to replace it all at this type old model?
      The only way to know is to call an HVAC company for an inspection of your old unit. 10 years isn’t terribly old and replacement parts should be available if it’s a major name brand, e.g. Carrier, Lennox, Trane, Bryant, York, Goodman and others.

  27. Shannon Chambers January 29, 2011 at 8:31 am - Reply

    I have a heat pump system with the top coil inside air handler. It was running continuously. I had a technician come out who told me it was the heat strips stuck on. He replaced them and the problem still persists. I called the same company back and they sent another technician out who said my outside condenser was failing due to the dust build up on the inside coils. This does not make sense to me. Could this be an accurate scenario?

    • Bob Jackson January 29, 2011 at 11:14 am - Reply

      It could be – how old is your heat pump and has it been serviced regularly in the spring and fall? The electric heat strips (similar to heater wires in a toaster) provide supplementary heating during periods of high demand or if the heat pump’s normal cycle can’t keep up, perhaps due to low efficiency if the outdoor temperature is very low. Did this happen during the recent arctic blasts that hit North Carolina in December and January?

      Dirt and crud buildup on the outside condenser coils blocks the airflow imparing efficiency. Air flow across the coils is extremely important for heat exchange.

      What may have happened is the very cold arctic air moved in, which makes the heat pump work harder due to the higher temperature differential between the outdoor and indoor air. However, the fins on the condenser coil are partially blocked with dirt/crud/dust restricting the air flow further reducing efficiency. The normal heat pump cycle can’t keep up with the heating demand and the electric heater strips kicked in. A secondary problem was the relay or circuitry for the heat strip is malfunctioning, causing it to permanently stay on.

      The scenario does make sense. However, you should complain to your HVAC company for not checking the outside condenser coil on the 1st service call to make sure the fins are clean and there’s no other maintenance issues.

      Take care to keep snow from piling up around the outdoor condenser unit (blocking the airflow) and it’ll stay clean longer if bushes are trimmed back at least 3 feet.

      See Heating and Cooling with a Heat Pump for a well done overview of heat pumps.

  28. Shannon Chambers January 29, 2011 at 12:17 pm - Reply

    Thanks so much for the response. At this point would cleaning the coils be sufficient to solve the problem or may it be too far gone? This did happen during the recent weather here in NC.

    • Bob Jackson January 30, 2011 at 8:51 am - Reply

      Condenser coils should be cleaned when necessary. A dirty coil makes the heat pump work harder, meaning it will run longer at lower efficiency and cause the electric heat strip to kick in. A heat pump with a really dirty coil where the fins that are totally clogged or nearly so won’t heat or cool and just wastes electricity.

      Since your first HVAC company didn’t perform a full system diagnostic to uncover all potential maintenance problems, have a different company – preferably one that sells your brand of heat pump with factory certified technicians on staff – perform an inspection and clean the coils if recommended.

  29. Dan March 3, 2011 at 9:18 pm - Reply

    I have a 1994 Coleman Evcon EB15B. The inside coils have some type of mold on them. The local AC repair place wants $200.00 to come do a chemical cleaning to the coils. If I was to do this myself, would I have to remove the coil from the house or is it possible to clean it in place? I’ve been looking at the Nu-Calgon Evap foam, but there was some kind of warning about taking the coil outside. I’m pretty sure I can spray a can of foam, but removing the coils is probably out of the question. Can you offer me some ideas?

    • Bob Jackson March 5, 2011 at 5:58 pm - Reply

      The AC coils can’t be removed without cutting the copper refrigerant lines, so it must be cleaned in place. The Nu-Calgon Evap Foam no-rinse coil cleaner is safe to use indoors and has a “pleasant lemon scent”. Make sure the HVAC system is off when you spray it on and wait until the foam has broken down and drained away before turning on the system. The Material Safety Data Sheet (MSDS) says “General ventilation normally adequate”, but you may want to open a window if you’re concerned.

      See my other response dated August 5, 2009 (scroll up) for a heavier cleaning with a pump-sprayer and acid-based cleaner.

  30. eileen mroz March 16, 2011 at 9:12 am - Reply

    I have a bryant a/c were the coils keep dripping water directly from them. They have been cleaned both professionally, which lasted about a year and they have also been cleaned using the cleaner you purchase from the home depot, which that has been lasting for about maybe a month. The water line is cleaned at the same time as the coils, so do I need to replace the coils?

    • Bob Jackson March 17, 2011 at 7:27 am - Reply

      I assume your Bryant is an updraft system with an A-frame evaporator coil. The condensate should stick to the coil fins and wick down into the condensate pan and drain off to the water line. The problem as you describe is the condensate is dripping straight down onto the blower motor and/or heater section instead of wicking down the coils.

      My guess is the bottom (i.e. upwind side) of your evaporator coils are “hairy”, meaning they’re contaminated with dirt, dust, mold or other foreign matter that disrupts the smooth surface of the evaporator fins and causes the condensate to drip off prematurely.

      Shine a flashlight at a low angle across the evaporator fins. Do you see a buildup of dirt, lint or mold on the face of the fins? If so, that’s your “hairy” problem and the coils need cleaning. Next shine the flashlight through the fins to a hand mirror on the other side to see if the spaces between the fins are clear.

      Can you tell what type of dirt is on the coils? Is it lint and dust or is it mold? If lint and dust, check that there are no leaks around the A/C filter and cabinet that’s allowing unfiltered air to enter the system. The dirt in unfiltered air will get caught on the evaporator coils. If mold, then try an acid based cleaner/disinfectant. Also give your coils a good shot of Lysol each time you change the air filter.

  31. eileen mroz March 20, 2011 at 6:46 pm - Reply

    Thank you for the info will give it a try.

  32. Do I need to replace the coil? March 30, 2011 at 12:44 pm - Reply

    Hi Bob,

    Your information is great – thank you! My house is 11 years old and we’ve been here about 2.5 years. To my knowledge nothing has been done to the furnace or AC unit. Everything seems to be working fine except in the summer our upstairs main room (larger with vaulted ceilings)NEVER stays cool. We literally lose sleep over this.

    My concern is my wife is pregnant with our first and the last thing I want is for it to hot to sleep this summer. I had a professional come and I was told we can replace the coil, but he was mainly trying to sell me a new furnace with variable speeds.

    Nice guy, but I don’t have 5k for this right now. Is this needed or will replacing or cleaning the coil allow more cold air to reach our upstairs basement.

    He was also saying our unit is big enough for our house. (not sure if he was just selling me) We have a basic unit, 80%, single speed for a 2600 sq house.

    Do you have any good advice?

    Thank You!!

    • Bob Jackson March 31, 2011 at 6:48 am - Reply

      First thing to do is check that the attic has sufficient ventilation and insulation above the main room with the vaulted ceiling. Install ridge vents on the roof if you don’t already have them and add additional soffit vents if necessary to match the ridge vent square footage requirements.

      Can you access the attic by the room with the vaulted ceiling? There must be an air gap between the insulation and roof for ventilation so air can flow from the soffit vents to the ridge vents (or gable vents if you have those). The air gap can be created by rigid rafter vent chutes so the insulation doesn’t seal against the roof deck.

      After verifying and/or correcting the attic ventilation and insulation, you may need to add air conditioning vents to cool the room as I did in this project: How to Add a Room Air Duct for Heating & Cooling. This particular bedroom above the garage had semi-vaulted ceilings for which I:
      1) Added a new HVAC air duct and ceiling vent.
      2) Added attic insulation.
      3) Installed ridge vents at a later date on the whole house.

      If you can’t install a new air vent in the ceiling then choose a location high on a wall at the far end of the room opposite the entry door.

      Please post back with what you find and decide to do.

  33. Robert May 19, 2011 at 10:25 pm - Reply

    Bob, great write up. I’ve been looking for info on this!
    We have a musty smell coming from a few registers which prompted me to inspect our air handler. I’m also planning to get our ducts cleaned as well. The inspection of the air handler revealed dirt build up on the coils. The unit itself is pretty old. I’ve been in the home for 12yrs and the home was purchased with the current unit. The prior owner was in the HVAC business. In terms of condition, my coils look very similar to your pic above, with the rust and dirt. I would like to post pics. Do you have a forum? How do I post pics?
    Anyway, I’m assuming cleaning the ducts will get rid of the musty smell. We’ve had rain for the last few days he and the smell have gone away but I still plan to have them cleaned. Also I cannot seem to locate the filter in the air handler. It was service a couple of years or more ago and I recall the service guy replacing a filter. I’d like to do it myself this time.

    When cleaning the coils is it necessary to protect anything?

    • Bob Jackson May 20, 2011 at 3:53 pm - Reply

      > I would like to post pics. Do you have a forum? How do I post pics?
      You should be able to reply to this comment on the web site and post pictures. There’s so much spam that this capability is normally disabled until I approve your first comment.

      > Also I cannot seem to locate the filter in the air handler.
      The filter should be there or perhaps close by on the main air return plenum.

      > When cleaning the coils is it necessary to protect anything?
      See the other comments for additional guidance, but you want to be careful the cleaning fluid is applied lightly enough that it wicks down the coils into the condensate drain pan instead of dripping onto the blower motor/fan or electronics.

  34. Sandeep May 20, 2011 at 9:50 am - Reply


    I have some problems with cooling at my home in the upstairs unit. I had a HVAC technician come and take a look at it and they said that their is a leak in the evaporator coil (They used some electronic sniffer in one of the coils to test this) in both ACs and charged up the system and recommended replacing the evaporator coil and the outisde condenser units. The units were probably installed in 1995 (when the house was build). I would appreciate if you could answer the following questions.

    1. Can the leak be fixed if its minor
    2. Was it a good idea to top up the units with freon given that there is a leak in coils
    3. Is it safe to use the AC if there is a leak in the evaporator coil. Is there any chance that the freon could get blown through the vents and cause potential health risks


    • Bob Jackson May 20, 2011 at 4:11 pm - Reply

      > 1. Can the leak be fixed if its minor
      Maybe – it depends on whether it’s a pin hole leak in a exposed portion of the coil tubing that can be plugged and soldered. Often a older coil develops pin holes due to corrosion within the fins where it can’t be reached, or more likely leaks in several locations. Given the age and condition of evaporator coils, new leaks will develop and you’ll spend more on repairs compared to replacing the coil. A proper solder repair will require draining the refrigerant first, adding to the expense.

      > 2. Was it a good idea to top up the units with freon given that there is a leak in coils
      Most leaks tend to be slow and topping it off with freon probably bought you a summer of decent cooling. It all depends on how quickly it’s losing refrigerant.

      > 3. Is it safe to use the AC if there is a leak in the evaporator coil. Is there any chance that the freon could
      > get blown through the vents and cause potential health risks
      R-134a refrigerant is inert, non-flammable and relatively non-toxic in low concentrations. Even if the coil blew out and dumped all the refrigerant, it would be diluted to level that you wouldn’t suffocate. If this WERE a problem I’m sure we’d see news stories about it. There are many many homes with minor evaporator coil leaks.

  35. Robert May 20, 2011 at 8:35 pm - Reply

    Thanks Bob. I don’t have the ability to attach a picture.

  36. Gary Schultz May 21, 2011 at 3:04 pm - Reply

    Same issue with a leak in the evapotaror coil. Attic unit is only 4 years old. Has signifcant corosion. Any idea whay a fair labor price should be to replace the coil? – the part is under warranty. Mechanic also suggesting a “new” device for 90 bucks,called it a corrision bomb – to help slow the problem in the future. Any opinion on that product? Thanks.

    • Bob Jackson May 21, 2011 at 7:07 pm - Reply

      Evaporator coil prices vary with the specific unit. Your best bet is to get three itemized quotes from reputable HVAC service companies and go from there.

      > Mechanic also suggesting a “new” device for 90 bucks,called it a corrision bomb
      The mechanic made a good recommendation. He was referring to a filter-dryer unit to remove any traces of water in the refrigerant. See An Up Close Look At Filter-Dryers for an explanation of how filter-dryers work.

  37. Chris May 27, 2011 at 10:44 am - Reply

    Great article….very helpful!
    Thanks for taking time to write it up and share.

  38. Silvia May 30, 2011 at 4:45 pm - Reply

    Thank you for the wonderful tips. I was trying to clean my coils with less toxic chemicals so I did a 50/50 vinegar and water combination. I am not sure how well it will actually clean it. I don’t know whether to turn my unit back on or give it a day to dry?

    Thanks again!

    • Bob Jackson May 31, 2011 at 7:07 am - Reply

      The active ingredient in white vinegar is acetic acid and most evaporator coil cleaners are either acid- or alkali based, but the similarities stop here.

      > I am not sure how well it will actually clean it.
      The problem with vinegar – aside from the really bad smell and funny looks from guests at the front door – is it’s neither a disinfectant or surfactant. A commercial coil cleaner disinfects to kill bacteria and mold, and contains surfactants which is key property of detergents to break down the dirt and wash it away. The foaming action of a no-rinse spray coil cleaner is an example of surfactants at work – wetting and breaking down the chemical bonds between dirt, oil and water.

      > I don’t know whether to turn my unit back on or give it a day to dry?
      I wouldn’t leave the vinegar on the coils more than 5 minutes.

      If you’re worried about “going green” use a product like Nu-Calgon Green Select® Evap-Green coil cleaner. It’s sold by

  39. Jim June 1, 2011 at 6:05 pm - Reply

    I bought two cans of the A Coil cleaner and put it on nice and heavy but it didn’t seem to do much. We had some one come out and they said it still needs cleaned,maybe with a bush or something. Would this really work or should I buy the two more cans again in hopes that works. ?

    • Bob Jackson June 1, 2011 at 7:37 pm - Reply

      The foaming self-rinse coil cleaner works best on coils that aren’t too dirty. First, assess the problem:

      1) Shine a flashlight through the fins onto a hand mirror to inspect how badly the fins are clogged.

      2) Buy a new garden pump sprayer with a spray wand, fill it with warm water, adjust the spray nozzle to a slightly open pattern. Turn off the A/C system. Place a plastic pan under the coils to keep the blower motor dry and catch the water. Spray the coils to knock out the dirt that’s between the fins. Spray gently (this isn’t a pressure washing) so as not to bend the fins, which would further block the airflow. Spray on the foaming coil cleaner and let it do its work. Rinse with the pump sprayer and reinspect with the flashlight and mirror.

      I say “buy a new pump sprayer” because you definitely don’t want to reuse a garden sprayer that’s had chemicals in it.

      3) Re-inspect the coils with the mirror and flashlight? Still dirty? Consider calling an HVAC professional to wash the coils with a acid- or alkali coil cleaner.

      See the Nu-Calgon Coil Cleaner Products for professional grade cleaners.

      I hesitate to advise brushing the coils because the fins are very thin and fragile. The bristles must be very soft and if you brush a bit too hard (it doesn’t take much!) the fins will fold over and block the air flow.

  40. Terry June 14, 2011 at 10:24 pm - Reply

    Bob, Great site, probably the most helpful I have found in regards to my issue..
    I had a tech come out and replace an outside fan switch after my unit stopped cooling. It is back to cooling like it was but my coils were filthy or hairy as you say. It is an upright in closet unit where the coils are in a W shape I went ahead and vacuumed along them without touching and got a lot of the debris off but there are chunks of debris close to the top of the peaks within the coil and the top half of the coil is still somewhat hairy. If I were to spray anything it would just drip onto the floor as just a filter is housed below the coils. Would a spray help me clean these coils and loosen some of the thicker debris?

    • Bob Jackson June 15, 2011 at 4:19 pm - Reply

      > If I were to spray anything it would just drip onto the floor as just a filter is housed below the coils.
      The foaming cleaner will stick to the evaporator coils and as the foam breaks down, will wick into the condensate drain pan. But if you’re talking about using a pump sprayer to forcefully clean the coils, then you will need to set a pan underneath the coils to catch the soapy water.

  41. Jean June 20, 2011 at 7:59 am - Reply

    I just had a tech out and he told me my coils were really dirty. He told me he would have to cut the coils out and do and acid wash on them, reinstall the unit and then recharge the system. Total cost $800. From what I have read above, it does not sound like the coils have to be removed to do the cleaning. Am I being scammed?

    • Bob Jackson June 20, 2011 at 8:28 am - Reply

      Coils do not have to be removed for cleaning. Recommend you get a 2nd and 3rd opinion from two other HVAC companies. The price range for a new 2 to 3 ton coil is usually in the $300 to $500 range, so for $800 you could have a new coil installed.

  42. Tray June 24, 2011 at 3:25 am - Reply

    My indoor unit is in a hall closet and it was difficult to remove the cover door because of the heaters exhaust vent and the copper piping. Once I got the cover off the coils looked like new albeit iced over. I used a whole can of cleaner,(WEB Coil Cleaner 14oz.) spraying both sides liberally. I too have a repairman wanting to cut out the “welds” and take the coils into the shop for cleaning. When i found this site I decided to do it myself.

    I had turned off the thermostat, breaker, and unplugged the unit and yet an eschusion ring for the heater vent pipe had come loose from the ceiling and I noticed it sparking when it touched the pipe. When I put the cover back on there were electrical sparks coming from the cover when it touched the copper piping too. Although I don’t get shocked when touching either. That reminded me that two nights before,(when the trouble started actually), we had a lot of lightning and one strike sounded like it was in the backyard but the lights didn’t even flicker. Sounded like a transformer blew but louder.

    The problem now is that the pipes are still freezing up. The other thing I noticed is that the house fan doesn’t work. The blower/fan works when the AC is on but doesn’t run otherwise. I mentioned that to the repairman but he never addressed it other than to move the switch from “on” to “auto”. Our unit looks much like the one in your picture. Blower on bottom, heater, and then coils. I believe the unit was installed in march of 2008 and it seems a bit soon to be having problems. Any recommendations?

    • Bob Jackson June 24, 2011 at 12:13 pm - Reply

      My recommendations are to have it professionally serviced to correct the electrical shock problem (!), fix the blower motor issue and run a health check on the entire system. The coils are freezing due to lack of air flow caused by one or more of dirty evaporator coils, weak blower motor or possibly a dirty air filter, but I suspect the HVAC tech would have replaced the air filter.

      How well did your coil cleaning work? Have you inspected the coils with a flashlight and a mirror to see between the fins? The electrical shock and blower motor problems may be related. Is your blower motor a single or two speed fan? If a single speed fan, is it running a full RPM? It could be the fan control circuit or the motor itself. An HVAC technician can diagnose these problems with the cost of a standard service call.

  43. Tray June 24, 2011 at 3:34 pm - Reply

    The technician that was out yesterday said the freon was fine and recommended the coils be removed and cleaned. After I told them I had cleaned the coils and they looked fine, a different technician came out and “sniffed” for leaks. While he did that he also filled the freon back up and reassured me that the problem was fixed. One of the fill caps going into the compressor had a leak “that took 3 years to cause a problem.” He teflon taped the threads and replaced the cap. I watched the line unfreeze as he filled it with freon. He said the fan not running was probably the thermostat and I felt pretty sure he was right about that,(it’s pretty flimsy/cheap),and told him I’d replace that myself.

    Overall I feel pretty good about how it turned out. I mean they could have taken the coils out and cleaned ’em and cost me a lot more than the $100 we got away with. I think we got off cheap and hope that doesn’t come back to bite me.

    Anyway, grateful for your site and I will check the fins with a light and mirror the next time I fool with the coils. The strange electrical spark I’ll have to see if I can reproduce and try to track that down. I’ll let you know what I find when I’ve replaced the thermostat. Thanks again for the site and info,..greatly appreciated.

  44. Rob June 29, 2011 at 10:46 pm - Reply

    My coils are pretty dirty and are located in the hallway of the house. The safest cleaner would be the foaming spray, but could I use a acid based cleaner( I already have some from cleaning the outside unit) if I open up the windows or is that too dangerous? Thanks for your help.

    • Bob Jackson June 30, 2011 at 6:11 am - Reply

      An acid-base cleaner for outdoor condenser coils isn’t necessarily an approved product for indoor coils as it may be stronger and create hazardous fumes that would be problem indoors. Always follow the manufacturer’s instructions and approved uses.

  45. Todd July 4, 2011 at 6:09 am - Reply

    Hi Bob,

    Thanks for all the good info. What a great service.

    I have a 1995 Lennox forced air in the basement similar to yours except the coils are encased by the plenum and I apparently only have access to the top coil sides which look great. I suspect they have not been cleaned for 10+ years however I have no freeze-ups nor air volume issues (but there could be restriction). There could be alot of junk on the inside surface. Can you suggest another path to get a small extendable mirror inside without dismantling into heat exchanger? Or shall I just relax and clean it with the foamy cleanser?

    Also, this was installed with no trap in condensate drain but install manual states there must be one. Shall I install one?

    Thanks again.

    • Bob Jackson July 4, 2011 at 8:55 am - Reply

      > Can you suggest another path to get a small extendable mirror inside without dismantling into heat exchanger?
      Unfortunately, that’s what you will have to do to inspect the bottom of the A frame coils.

      > Also, this was installed with no trap in condensate drain but install manual states there must be one. Shall I install one?
      It depends on where the drain line is going. If it empties into the home’s drain plumbing, then you’ll need a trap to keep out the sewer gases, flies, mosquitoes, etc. The condensate drain pipe for the air handler in my attic does not have a p-trap because it empties to the outdoors as shown in this photo. It’s downhill all the way from the attic and empties to the outdoors. I extended the pipe about 8 feet from the house to avoid a wet spot by foundation which can invite termites and other pests. Freezing isn’t a problem because the air conditioner only runs in warm weather.

  46. Betti July 7, 2011 at 11:52 am - Reply

    HELP! I have an older Bryant heat pump located under my home. It is a horizonal unit .. and I noticed the condensation leaking from all under the unit. I removed one panel and found the blower area was filled with water .. which ran out once the panel was removed. When I tried to remove the panel with the coils and condenser tray .. I found someone had glued the tray connector to pc pipe for the drain. I couldn;t unscrew the PVC and we ended up breaking the connection from the tray to the PVC. What a mess. I cleaned the over flowing tray and the coils. But now I have no way to connect anything to the tray for water to leave the tray .. I have read where you should replace tray and coils… but this is very expensive. I have brain stormed glueing something to the tray and running some tubing from the tray throught the hole to run the condensation away from the unit.. or drilling a hole in the tray and through the bottom panel and have the condensation drip below… any help any thoughts .. ??

    • Bob Jackson July 7, 2011 at 5:32 pm - Reply

      A couple of photos from different angles of the broken PVC condenser tray would help so I can better understand what exactly is broken. If the pipe nipple molded into the condensate tray is broken, you should be able to glue it with PVC primer and glue. Turn off the system, dry everything off and prime and glue the pieces back. You can do almost anything with PVC with the right set of fittings.

  47. Jordan July 12, 2011 at 4:58 pm - Reply

    Could a bad vibration coming from the evaporater area in the attic be caused by dirty evaporator coils? It just started yesterday, sounds and feels like a helicopter hovering over my house every time the A/C turns on. The system is 6 years old and I’ve never cleaned my evaporator (but I do clean the outside condensor every year).

    Maybe it’s a loose fan blade or something? My wife put a dryer sheet in the filter when she changed it (to make it smell better), only problem is she put it on the wrong side and it got sucked into the system. The filter is about 20 feet away from the evaporator/blower unit. I can’t imagine a dryer sheet would cause this though, could it?

    Excellent write-up by the way, thanks!

    • Bob Jackson July 12, 2011 at 6:49 pm - Reply

      > My wife put a dryer sheet in the filter when she changed it (to make it smell better),
      > only problem is she put it on the wrong side and it got sucked into the system.
      The awful helicopter sound and vibration is because the dryer is sheet stuck in the squirrel cage blower fan.

      Shut off the power at the circuit breaker, open the sheet metal cabinet and fish the dryer sheet out of the blower motor. If you don’t, the dryer sheet will be shredded and the debris will cake the inside of the evaporator coils obstructing the airflow.

  48. Scott (Arkansas) July 18, 2011 at 10:20 pm - Reply

    Bob, great post. Our home is set for 78 degrees and we have not been able to cool it below 80 for 5 hours of the day with the 100 degree heat. Had a buddy who owns a heating air business come out today. I have a 3.5 ton 10 seer 17 yr old Ruud unit outside. The copper was cool but not “beer can cold” and sweating. He decided to add 1.5 lbs. of freon and he said it could use a little more. Instantly it was cold and sweating. This happened at 2 pm this afternoon. By 10 pm this evening, I now feel warmer air blowing and our home is 85 degrees.

    I followed your directions (excellent by the way) and looked at my condenser coils for the first time in 17 years. I am proud to say they looked as clean as yours and identical with the copper wear and tear. I clean my filter constantly. What do you think I should do? When momma ain’t happy (and cool) ain’t nobody happy. :o)

  49. Scott (Arkansas) July 18, 2011 at 10:31 pm - Reply

    Let me add that after I just turned my system back on, the internal blower kicked in, but the outside unit is not running at all. I checked the fuse box and both of the units are on the same one. What do you think is going on Bob?

    • Bob Jackson July 19, 2011 at 4:46 am - Reply

      You need to call a HVAC service company to get the system checked.

      If the outside condenser unit isn’t running, the most common problems are:
      * Bad capacitor – provides extra current needed when the compressor motor starts. These are not expensive.
      * Compressor – could be broken or overheating. Overheating will cause a thermal protection shutdown. Expensive to replace, system won’t cool.
      * Bad fan motor – are the fan blades turning? It’s possible the compressor is running but the fan motor is broken. System cools poorly.
      * Refrigerant – low refrigerant charge due to a leak. An AC guy will check the high and low side pressure values.

  50. Wilson July 19, 2011 at 10:47 am - Reply

    I have a 6 y/o A/C that was not cooling like it should. The technician came out and tested for leaks. He said the coil was leaking and needed to be replaced for a cost of $1694.00. He said he would have to drain the refrigerant, then replace the 9 lbs, along with replacing the coils. Is this price a rip-off?

    • Bob Jackson July 19, 2011 at 5:31 pm - Reply

      It could be a fair price for replacing the evaporator coils, without knowing the specifics of your AC system it hard to be certain. Replacing the coil in a 2 ton system will be less expensive compared to a 3 ton. Labor will be the same, but the evaporator coil part cost will be different. Best to get 3 estimates from reputable HVAC service companies with equivalent warranties on parts and service. I will say if it’s a 3 ton system then $1700 sounds high, you could replace the entire air handler for that price.

      Please post back with what you decide to do.

  51. Jordan July 22, 2011 at 11:08 am - Reply

    Just wanted to update you that the dryer sheet was stuck on one of the blower fan blades. I can’t believe such a little weightless item can cause so much noise and vibration! Thanks Bob…next task is to clean up my evaporater coils using your writeup. Hopeing for the best since it’s only 6 years old.

  52. SSebastian July 22, 2011 at 12:05 pm - Reply

    Hey Bob…

    First I wanted to say… great advice!

    I just bought my first home about a year ago.

    I have a 1500 sqft ranch that is about 60 years old. The furnace and AC units are roughly 20 years old. I’m thinking about replacing both to newer energy efficient models (I know I won’t save much on my energy bills since they aren’t that high to begin with compared to the cost of brand new HVAC units). BUT, I believe my conformt level would increase and so would the value of my home if and when I sell it.

    My question to you: Does it make sense (financially) to have both installed at the same time?

    Thanks again!

    • Bob Jackson July 22, 2011 at 6:07 pm - Reply

      > Does it make sense (financially) to have both installed at the same time?
      I am led to believe by your description that you have separate furnace and air conditioning systems, correct? Since you live in the great state of Minnesota with mild summers and cold winters, your annual heating demands are much greater than for cooling. Your priority should be replacing the 20 year old furnace with an energy efficient model for the fastest payback on the cost of heating your home, especially with the high price of carbon fuels.

      See the Lifecycle Cost Estimator for an ENERGY STAR Qualified Gas Residential Furnace to determine your annual savings and payback in years.

  53. Steven Swann July 22, 2011 at 4:40 pm - Reply


    This is great stuff. Thanks for having done all of this work.

    As a native Floridian, I’ve grown accustomed to a steady decline in the quality of work folks have done for us over the past 20 years.

    Our current joy surrounds the TWO thermostats which were apparently set up to operate the same A/C unit in one part of our house when we built it in 2008.

    The contractor who installed the unit tells us not to operate one of the units (and we don’t), because when both thermostats are on, the system either cools the house down to 65 degrees, or heats it up to 80 degrees.

    What is going on? Can we re-engineer this?

    Thanks again.

    • Bob Jackson July 22, 2011 at 6:25 pm - Reply

      Two thermostats wired to the same AC unit? Where are the thermostats located, e.g. upstairs and downstairs?

      What you need is a single thermostat to control the AC unit with a remote sensor. The remote sensor is placed in another room (e.g. upstairs) that you want to keep comfortable to measure the temperature at that location. The remote sends it’s temperature status to the main (master) thermostat, which is sole control interface wired to the HVAC system. This prevents the conflict between two “master” thermostats.

      You can install this yourself, or hire a HVAC tech to install it for you:
      White Rodgers 1F85RF-275 80 Series Wireless Remote Sensor Kit

  54. Larry West July 29, 2011 at 11:22 am - Reply

    Thanks Bob for the great help. My question is about air filter replacement. I have the Aprilaire (5or6 in. thick). We vacuum in 6 months and replace each year. Is this normally enough in a fairly clean 1600sq ft home

  55. Rob August 31, 2011 at 6:31 pm - Reply

    I have the same setup as you, thanks for making this guide!

    One question, is it normal for cold air to blow out near the two blue plugs located at the bottom right while the air conditioning is cooling the house? I have noticed an increase in cold air flow coming out the bottom right of the unit.

    • Bob Jackson September 1, 2011 at 4:26 am - Reply

      Air should not be blowing around the blue plugs in the condensate drain pan. The plugs may be loose or cracked and need to be replaced to prevent a water leak.

  56. Don September 2, 2011 at 10:42 pm - Reply

    Bob, I have a 3 ton Lenix, unit. The unit was not blowing cold so I had a tec come out. He checked the unit and saw some oil on the coils. He cleaned the coils and check the pres on the unit. It has been working for about 10 days and is now blowing warm air. I checked the coils for any oil and they are clean, but when I run my hand across the coils, they feel warm with just a few of them feeling cold. Is this normal, or should the whole coil feel cold during operation.

    • Bob Jackson September 2, 2011 at 11:54 pm - Reply

      Is the fan on the outside unit (condenser/compressor) running?

    • Bob Jackson September 5, 2011 at 7:38 am - Reply

      Don e-mailed:
      > The fan and the compressor are running and I have rechecked the coils for any more
      > oil after the cleaning. No oil leak, everything seems to be running, but the system will
      > blow cold for a week and then blow hot air. If I shut it down for a few hours, it will blow
      > cold again for a week before it does it again.
      Call your HVAC company back and ask them to be ready for a quick house call the next time the unit stops blowing cold air. With the system still blowing warm air, ask the technician to verify the compressor is working and the refrigerant pressures are within spec. If the pressures are out of spec, you have a leak. If not, then I’m thinking the compressor is overheating and going into thermal protection shutdown. Turn the system off, remove the noise insulation jacket from the compressor (if there is one), let it cool down for 45 minutes, then restart the system. If you have cold air, then you need a new compressor. Since the refrigerant will have to be evacuated, have a dryer/filter installed on the liquid line to catch any moisture and contaminants as an extra precaution – these aren’t expensive.

  57. Mike Jacobson September 3, 2011 at 12:16 pm - Reply

    To Don..oil on coils usually indicates refrigerant is leaking from your system. The compressor requires lubrication and oil travels through the system with the refrigerant. When a leak occurs, oil and refrigerant escape. If the unit ran for less than 10 days and is not cooling, you could have a fairly large leak. Leaks in the outdoor condenser coil can sometimes fixed by a professional, but usually replacement is the best option.

  58. Tony September 5, 2011 at 7:47 pm - Reply

    I am having an issue with condensation building on the outside of everything a/c related in my attic where the air handler is. (electric air handler that blows horizontally in a hot FL attic)
    The main distribution outflow box, the flex ducts going to my vents, the condensate drain line.. everything has water building on it which then drips on my insulation. The backup drip back is empty and dry and I’ve insulated the condensate drain line, but I don’t know what to do for condensation building on the outside of the ducts.
    A friend told me that a dirty evap coil could cause the system to run harder, which forces everything to run colder and build condensation. Is this likely the problem?

    • Bob Jackson September 6, 2011 at 6:40 pm - Reply

      A really dirty coil will cause the system to run longer and block the air flow. The humidity and dew points are so high in the Tampa Bay area that it wouldn’t take much of a temperature drop due to “cold soak” to cause condensation if the system ran all the time. Also check for air leaks in your duct work – loose joints, tape, etc. I lived in south Florida for 16 years, owned 3 different homes and replaced the AC units in two of those, but never had a problem as you describe. Definitely get a full system health check by a HVAC tech.

  59. Ralph Black September 8, 2011 at 12:18 pm - Reply

    Thanks for this post it has helped take care of a mold problem I had been having on the coils. Was afraid to use anything on the inside unit. Thanks again. Pictures and text very infomrative.

  60. Tim Dabrowa September 14, 2011 at 2:10 pm - Reply

    The access panel to the Evap coil is blocked for no access due to upgrade kitchen hood ductwork at my restaurant. right in front of the unit!!
    Can I cut out a new panel in the back, and replace with sheet metal to fit and screw in and tape up?

    • Bob Jackson September 14, 2011 at 8:08 pm - Reply

      You can cut a new panel on the back of the coil casing. Take special care not to damage the coils – a small puncture will cause all the refrigerant to leak out and you’ll have to access the front panel to repair or replace the coils!

      Drill a 1/2″ starter hole very carefully in the back corner of the coil case, push on the drill bit gently so it doesn’t get away from you and over penetrate when you punch through the sheet metal. Use tin snips to cut out the panel – don’t use power tools (nibblers, metal saws, etc.) because those will create a shower of metal shavings inside the case and get all over the coils. Tin snips will allow you to cut out the back panel as a single piece. Vacuum out any drill shavings made by the starter hole that got past the insulation glued to the inside of the panel.

      Be sure to cut the replacement panel at least 3/8″ larger than the hole and insulate the panel. Use a couple sheet metal screws to secure it, then seal it with HVAC tape. See my other comments for air handler insulation sources.

      Consider hiring a sheet metal specialist to do the job. There’s a real talent to what those guys can do – the new panel would look like it was factory made. I know if I went at it with tin snips the cut would be a bit warped.

      At some point, you will have to get to the front of the unit for maintenance or replacement. You may want to consider a modular way to disconnect the kitchen hood first before cutting open the coil casing.

      Good luck!

  61. Cliff October 1, 2011 at 12:21 am - Reply

    I have a nordyne CLQA 036U B unit in a 16×80 mobile home. During the last part of this past winter,the blower fan sometimes would hum and not start. If I caught it in time,I could open the access panel and give it a spin to help it get started and it would run until the house came up to temp and cut off. If I didn’t get to it, it would trip the thermal switch and I’d have to turn the unit off long enough to allow the motor to cool off. Then give it another manual spin to get it going again. I’ve been doing the same this summer as well. Should I replace the motor? If so, could you please tell me what motor I need?Where to get it(ebay or amazon preferred)

    Thank you, Cliff

    • Bob Jackson October 1, 2011 at 5:18 am - Reply

      The fan motor starting problem (hum but won’t spin) sounds like a bad starting capacitor. Nordyne doesn’t publish their parts diagrams. You could try UNITED PART SUPPLY which sells Nordyne capacitors. At the United Part Supply page:
      1) Select “capacitor” part type
      2) Enter your model # CLQA 036U B
      3) Click search.

      The results show three parts: Capacitor-dual (fan & compressor): Capacitor-single (compressor only) and Capacitor-single (fan only). You might call a HVAC company and ask for their recommendation, they might share some advice – especially if you schedule a health check service call.

      Not sure if you need the “dual” or “fan only” capacitor. Take a look at your air handler and see if have one or the other. Be very careful with capacitors – they are high voltage items, don’t touch or short the terminals.

  62. Cliff October 2, 2011 at 9:33 pm - Reply

    Thanks for the super quick reply. There is a capacitor connected at the blower housing with only two terminals.I am assumeing that this would make it a single(fan only)capacitor.The stock number on the capacitor is POC7.5 Should I order the Packard POC7.5 377 Volt 7.5 MFD Motor Run capacitor?

    Thank you again, Cliff

    • Bob Jackson October 3, 2011 at 6:39 am - Reply

      The part “# Packard POC7.5 377 Volt 7.5 MFD Motor Run capacitor” is a big help. You can order it from

      You can’t go wrong for a couple of dollars, so replace it as the mostly likely cause of the stalled fan motor.

  63. Adrian October 3, 2011 at 2:24 pm - Reply

    This may be a stupid question, but I have heard that you should never run the A/C and the heater on the same day (or within around 24 hours of each other) as the rapid changes in temperature can crack your evaporator coils. Is there any merit to this?

    • Bob Jackson October 3, 2011 at 6:35 pm - Reply

      An odd question, especially since your company manufactures building automation systems, including HVAC controls, but OK.

      It should be a rare circumstance that a home HVAC system requires an immediate change over from heating to cooling. Such an abrupt change means there’s something wrong with the house insulation or envelope. I can see heating on a cold night and when the day warms up, turning on the AC; but that would require hours of gradual warming when no heating or cooling is needed and there’s no risk of thermal shock to the evaporator coils.

      There are thermostats that will automatically switchover from heating to cooling modes (and vice versa), but those have a deadband of several degrees so the two cycles aren’t in conflict.

      The question reminds of episode of the Muppet Show when Scooter put the Eskimos and Arabs in the same dressing room.
      Later, Scooter yells down to Kermit: “I got trouble up here boss!”
      Kermit: “What?”
      Scooter: “The Arabs and Eskimos are sharing a dressing room.”
      Kermit: “So?”
      Scooter: “So the Arabs want it hotter and the Eskimos want to turn on the air conditioner.”
      Kermit: “…Try to get them to compromise.”
      Scooter: “Oh they have compromised! The Eskimos turned on the air conditioner and the Arabs set it on fire!”

  64. Rick Forschner November 25, 2011 at 9:25 pm - Reply

    About six months ago we replaced our ten year old Ruud system with a Lennox…both 3.5 tons. Three months ago we became aware of a musty smell. We called the installer. He noted the pan was not fully draining. He corrected and cleaned mold/mildew from the coils. This past weekend we became aware of the smell again. We are waiting to hear back from the installer (it’s Thanksgiving weekend). Should we be concerned? What do you recommend? (other than this one issue the unit seems to cool and heat better than our old Ruud)

    • Bob Jackson November 26, 2011 at 9:12 am - Reply

      > He noted the pan was not fully draining. He corrected and cleaned mold/mildew from the coils.
      Condensate pans are sloped to direct the water to the collection tray where it flows into the drain lines – a simple gravity fed arrangement. Your system was not install correctly if the condensate pan was not fully draining – was the unit not level or the drain piping not sloped downward? I question if the condensate drainage has been fully “corrected” and recommend calling another factory certified HVAC company to inspect your system. There shouldn’t be standing water in the condensate drain pan, check the drain lines are clear and the condensate pump (if any) is in good order.

  65. Larry Spires December 4, 2011 at 11:36 am - Reply

    My compressor on a 4 ton coleman heat pump overheated and went to ground. Unit 4 years old. Tech said he could replace compressor and flush system and all would be fine. 4 months later same thing happened. I noticed that the TXV sensing bulb was detached from the refridgerant line on the outside unit. I pointed this out to the tech. and he stated that it would not cause the problem. He now suggest a whole new system. Any comments?

    • Bob Jackson December 4, 2011 at 1:16 pm - Reply

      > I noticed that the TXV sensing bulb was detached from the refridgerant line on the outside unit.
      > I pointed this out to the tech. and he stated that it would not cause the problem.
      The thermostatic expansion valve (TXV) won’t work properly if the sensing bulb is not in direct contact with refrigerant line so it respond to the temperature changes and provide feedback to the TXV valve to regulate the flow of refrigerant. The TXV valve plays a role in protecting your compressor, too.

      I’d get a 2nd opinion because a detached sensing bulb is a red flag for improper installation. You may have a 5 year warranty on the compressor, so have everything thoroughly checked.

  66. Rick Schreiber December 19, 2011 at 2:10 pm - Reply

    Hi Bob – Thanks for this article and your great responsiveness to answering follow up questions.

    I’m in the middle of a basement remodel project. Since heating season began in NY, I’ve noticed that my furnace hits a temperature limit during normal operation – the heat cycles on for 5 minutes, then off for 2 minutes). This happens several times while blower keeps running. It also seems to take a lot longer to get the house up to temperature.

    I have central air, and it was suggested to me that it’s likely that some of the destruction/construction debris has entered the system and clogged the coils.

    I was going to use the foaming cleaner since I don’t have access to underneath the coils, but I didn’t know if it was appropriate to use that product during heating season, since the coils won’t self clean via condensation.

    Also had another idea; would it be reasonable to use compressed air from the top of the coils and a vacuum connected to the condensation drain to clean the coils? My thought is that the compressed air would dislodge the “hair” and the vac would remove it.

    • Bob Jackson December 20, 2011 at 9:48 am - Reply

      To summarize the symptoms:
      * Blower runs continuously
      * Heat cycles on 5 mins, then off 2 mins
      * House won’t warm sufficiently
      * Concern the AC coils may be dirty from recent construction, restricting the airflow

      Were the return air ducts open during the remodeling such that air bypassed the air filter? If not, the air filter should’ve caught the construction debris/dust. Check the air filter isn’t dirty and replace it if necessary. Have you opened the air handler to inspect the coils by shining a high intensity flashlight through the coils to a mirror on the other side to see if they’re clogged or dirty? If the coils are in fact that dirty, your blower motor could be clogged and blowing weakly. I wonder if the dirt/dust may have built up on your flame sensor and burners, too?

      If the return ducts were never open to unfiltered air, then I tend to think the problem isn’t with dirty coils or blower motor. But you can use the foaming coil clean as it’s self rinsing. Just leave the system off for 15 mins so it can wick down to the condensate drain pan.

      AC systems are relatively safe to work with because there’s no flame, heat and natural gas or fuel oil as with a furnace. Furnace problems should be looked at by a certified HVAC tech. Assuming the coils aren’t restricting the air flow, you could have a problem with the thermostat, flame sensor, blower motor or other furnace electronics. Heat cycling on & off every 7 mins (~8.5 times/hour) is not normal.

      Please post back with what you find.


  67. Curtis December 28, 2011 at 1:16 pm - Reply

    My A-coil lays sideways and I cannot gain acess to the lower part of coils. Do you think the foam coil cleaner sprayed on top coils will drip downward and help clean the lower coils ? I might be able to use the AC flow cleaner that has pump spray nozzel and slide my hand between opening and pump that type in the inside but not much room to get my hand in there.

    • Bob Jackson December 28, 2011 at 8:08 pm - Reply

      The foaming coil cleaner spray can will shoot the cleaner a good 3 feet, so it’s not necessary to be directly over the coils at the far end where it’s widest. A pump sprayer and wand will do even better by forcing a gentle stream of cleaning fluid through those hard to reach areas.

      Does your horizontal A-frame evaporator coil look similar to this Goodman model? Can you get to both sides of the A coils?

      If your challenge is getting access to the other side of the horizontal coils, consider installing a duct access panel in the plenum in front the coil case. Lau Industries and Kees make duct access panels. These are insulated duct access doors with a gasket to seal against the plenum and metal tabs (similar to a duct starting collar) which grip the inside of the plenum to prevent blowouts. Easy to install in the rigid plenum ductboard.

  68. Rick Schreiber January 9, 2012 at 7:53 am - Reply

    To clarify, the house does eventually reach temperature. It takes longer than it did before the remodel, and the gas heat source turns on and off several times during a single heating cycle, running for 4-5 minutes, then off for one minute.

    I tried the flashlight and mirror tip and I was able to see light coming through the A-frame at several locations, so I guess it’s not clogged

    Also, the return was never opened to unfiltered air.

    I had a tech look at it and he said the computer indicates that it’s shutting down the heat on limit, which tells us that the plenum is overheating.

    We took the bottom door off to allow more air flow and that seems to have alleviated the problem, so I’m moving forward with adding more returns.


  69. Mary Ellen March 13, 2012 at 6:18 am - Reply

    Having just moved into a rental condo unit and found that it smelled damp and musty every time a/c would go on, I used your video to figure out how to clean evap coils with no-rinse foam cleaner from Home Depot. I cleaned all registers and return grills. My question however is that once I removed the return grill, I found lots of dirt inside. I vacuumed the return box to remove loose dirt, but is the darkened areas mold??Condo is 3 years old, but probably not well taken care of since there have only been renters. Should the return box (yellow fibrous material) be cleaned to make it yellow again. If mold, can I spray bleach on it?? Thanks for help. I hate to bother landlord for this, don’t want to be a bad tenant and can do myself.

    • Bob Jackson March 14, 2012 at 5:44 am - Reply

      I would bother the landlord and insist that proper maintenance be done. You’re paying to rent a condo in good condition and from your description it appears the AC unit has long been neglected. Living in Florida, you really need a sanitary AC unit.

      Start with a polite phone call to the landlord and if nothing is done, send a certified mail letter explaining the odor, health concerns, etc. Read your rental agreement for terms relating to maintenance, upkeep, reporting and notification requirements. Keep detailed records of all communications in case you end up in small claims court or breaking the lease.

      > Should the return box (yellow fibrous material) be cleaned to make it yellow again.
      The yellow rigid fiberglass plenum liner often has a black top layer. A white or grayish coating may be dirt or mold. I spray Lysol disinfectant on my plenum liner and AC coils – do while the air handler (fan) is running to pull the Lysol into the ductwork and disinfect that too. I’ll put half a can of Lysol into my air handler and ductwork this way. Open the windows so the place can air out.

  70. Mich Cook March 23, 2012 at 12:21 am - Reply

    Bob, an absolutely brilliant service !! A mate has asked me to troubleshoot his unit because of successive (3) failures by pro outfits to eliminate the flooded ceiling syndrome. Inspected – a) the coils drain pan is correctly inclined and flows all water to drain. b) drain now has 7% fall and P-Trap removed for good measure. c) evaporator coils and finning (crossflow) appear clean. c) a secondary drain pan will be installed as a precaution after the primary problem is fixed.
    Observation – condensate from coils is to a significant degree being dragged off by air to fan and splashing onto plenum floor and fan.
    Question a) – a sign of fan speed too high?? (original installation was just a bit too pushed to be effective and so it’s suspected fan speed was increased) and if yes, do I best just throttle fan speed until condensate lands where it should or use an instrument to measure (a suggested) air velocity P down to 2.0metre/sec max?? Best instrument for this type of measuring, url?? b) sealing of the plenum ? as I notice (hanging) bolt holes, small splits (duct joint)and the drain opening as places that can allow air to be sucked into the plenum after the evaporator – will this air condense in the colder and high P plenum??
    Thanks in advance

    • Bob Jackson March 25, 2012 at 9:50 am - Reply

      I wonder if the AC system is too small for the house in terms of total BTUs or tons? (12,000 BTU/hour = 1 ton) An undersized AC system would explain the persistent high humidity and heavy condensate on the evaporator coils; and the too-high fan speed in an attempt to move more air to cool the home. As you said, the too high fan speed is blowing the condensate off the coils onto the fan and plenum floor.

      Your description of the bolt holes, splits in the ductwork and improperly sealed drain opening are indications of poor quality workmanship when the system was originally installed – which reinforces my belief your mate got an “economy job” and undersized AC system.

      My recommendations are:
      1) Reset the fan speed to factory recommended speed.
      It’s not clear how the fan speed was increased – was the blower motor replaced? Most AC systems have a single fan speed that can’t be adjusted by the homeowner, it’s either ON or OFF. You can buy digital air flow meters on for around $150, but I would focus on restoring the factory recommended fan speed and skip buying a air flow meter that you’ll probably never use again.

      2) Yes – do seal all leaks in the ductwork, plenum and air handler. This is very important to keep out dust/dirt and increase the efficiency of the HVAC system.

      3) Buy one or two portable dehumidifiers for the home, get a minimum 70 pint unit. The dehumidifier will help compensate for the undersized AC system because dryer air feels more comfortable. I’ve had good results with the Frigidaire 70 pint model. Frigidaire FAD704DUD 70 Pt. Dehumidifier

      If your situation allows, the dehumidifier can be piped to a drain line and never worry about emptying the condensate bucket.

      Let me know what you decide to do and how it works out.

  71. pablowablo April 15, 2012 at 8:05 pm - Reply

    it looks like you just serviced the clean side of the A coil. isn’t the underside where the dirt collects?

    • Bob Jackson April 16, 2012 at 7:40 am - Reply

      Yes, dirt will tend collect on the inside (upwind) part of the coils first. However it is very difficult to access the interior of the A-frame coils in most air handlers without taking the gas burner and/or fan sections out – a major project best left to the pros.

      If you’re keeping up with spring and fall seasonal maintenance, changing the air filter regularly and have no leaks in your duct work that bypass the air filter, then the spray foam cleaner as shown here should be sufficient. The cleaner will coat both sides of the coils to clean and disinfect.

      Per my other comments to readers, you can shine a flashlight through the coils to a mirror on the other side to get an idea of how dirty the inside of your coils are. A heavy cleaning will involve stronger chemicals, a pump sprayer and wand to force a stream of cleaning liquid through the coils to better dislodge dirt on the underside of the coils. If your system is dirty enough to require a heavy cleaning, I recommend calling a professional HVAC company for a full system health check and cleaning.

  72. Jeff April 19, 2012 at 4:47 pm - Reply

    My air intake is in the ceiling and I’m able to get up behind the filter. I just removed a layer of damp dirt from the coils. It peeled off like soft paint. Can I use a foam cleaner from this side only?

    • Bob Jackson April 19, 2012 at 5:19 pm - Reply

      The foam cleaner can be used on your coils. Wear safety glasses so it doesn’t get into your eyes while spraying overhead. Given that your coils were plastered with a solid layer of dirt, I would have an HVAC company take a look at your system as it seems not to have had regular maintenance.

  73. David May 1, 2012 at 10:16 pm - Reply

    Hi Bob,

    Thank you for the great article. I went to Grainger Industrial Supply and bought two cans of Nu-Calgon Cal-Spray evap-fresh to clean my evaporator coils.

    I have two units that are both horizontal A-frame. I opened the access panels and there’s not much room to get to the bottom side of the coils. I don’t want to cut out and install an access panel. Is there another way to get to the bottom? Even the top, I don’t have that much room.

    Also, after the foam cleaner has done its job, when is it safe to turn the AC on? I read somewhere that I should run it for some time after the cleaning is finished so that the condensate water will rinse the coils. When and How Long should I run the AC units for?

    Thank you very much for your help.

    • Bob Jackson May 2, 2012 at 6:52 am - Reply

      There are two styles of horizontal A-frame evaporator coils: 1) The A frame lies flat on it’s side like an traffic arrow marked on the highway, 2) The A frame is mounted sideways like a less than symbol < . Configuration #1 provides is a bit easier to clean because the faces of the A-frame are vertical and some units have removable side panels. I'm thinking you have configuration #2 where it's more difficult to access the downward facing side of the A-frame <.> I don’t want to cut out and install an access panel.
      Cutting an access panel in the sheet cabinet isn’t a big deal, you do have to be careful not to damage the coils. A sheet metal professional can do the job, it’s not expensive and it’ll look like it was factory installed. Short of cutting an access panel, a pump sprayer and wand can reach into those far crevices and pinch points.

      > Also, after the foam cleaner has done its job, when is it safe to turn the AC on?
      The foaming cleaner breaks down quickly and you’ll see it run off into the condensate drain pan. 10 to 15 mins should be plenty for the cleaner to do its work. What you want to avoid is turning the AC on too soon and blowing the foam off the coils.

  74. Kathy May 4, 2012 at 1:53 pm - Reply

    Love your advice. I have used 3 cans of Web coil cleaner on both condenser coils and evaporator coils. Evaporator coils had not been cleaned in 10 years and I still have a problem. If ac unit is set below 70 degrees eventually I have no air coming out of vents. This happens at night as this is when I turn the thermostat lower. Unit runs but no cool air. Should I try cleaning the coils again or what? I am a widow with a fixed income and really don’t have money to call in a tech. Also are “paper” filters required or even a good idea for this type ac unit. I have coil filters and have cleaned those. My unit looks just like the one in your pictures but it is electric.

  75. Kathy May 4, 2012 at 1:55 pm - Reply

    Also forgot to mention if I shine an LED flashlight through the coils from the bottom very little light shines through.

    • Bob Jackson May 5, 2012 at 9:27 am - Reply

      > If ac unit is set below 70 degrees eventually I have no air coming out of vents.
      > This happens at night as this is when I turn the thermostat lower. Unit runs but no cool air.
      Your evaporator coils are freezing up at night and blocking the air flow.

      Evaporator coils are a heat exchanger – the cold refrigerant in the coils absorbs heat from the incoming air forced through the coils by blower motor. The air is cooled and the coils are warmed. Clean evaporator coils are necessary for good airflow and to keep the surface of the coils above freezing (32 degrees F). If the coils are dirty, the airflow can be reduced to the point the coils aren’t “warmed” sufficiently causing the water condensate to freeze on the surface of the coils, completely blocking the airflow. Once the coils freeze up, the process accelerates since there’s no airflow to warm the coils. The only solution is to turn off the AC system, wait for the coils to thaw and clean the coils.

      During the day the incoming air from the house is just warm enough to keep the dirty coils from freezing.

      At night, the incoming air is cooler and the dirty coils freeze up.

      You really should call in an HVAC technician to thoroughly clean the coils and check the system health. The coils will need a deep cleaning with a pump sprayer and stronger chemicals. Let the pro do it because you run the risk of getting your motor and electronics wet, causing a bigger problem.

      I use the disposable Filtrete™ air filters on my air handler with excellent results.

  76. John May 23, 2012 at 9:30 am - Reply

    Great info, thanks! I have a horizontal attic unit by York. I noticed water stains on sheetrock in a bedroom. After inspection the unit is leaking. I had 2 differnt techs come, one wanted to replace the whole system for 5k the other just the coil and drip pan for 2.5k. They both said the drip pan is rusted and leaking. The second added I could try patching it with silicone and see if that lasts as other than that the system works. My dilemma is that I cannot find pictures of a horizontal unit in an attic like mine in order to tell where the coil and drip pan are! Major novice, yes. But, I would like to give it a shot as it may solve the problem for as long as a couple of years and money is tight right now! Any suggestions/pictures of this type of unit? Thanks!

  77. Eric Pham May 26, 2012 at 8:43 pm - Reply

    I have the AC unit on the attic (BPD division of Carrier Model 506B042)

    I just read your reply to Rick Forschner about standing water in the drain pan. My problem is that the pan is not sloped properly. How can I fix it myself? Can I prop it up so the pan can drain correctly. Note: The attic is very tight. I have a hard time to lift the unit. Thanks.

    • Bob Jackson May 27, 2012 at 7:41 am - Reply

      The Bryant Air Conditioner instructions you provided state:
      “4. Install coil so that it pitches slightly (1/8 inch) toward the condensate drain opening. Coils have drain opening on one side only.”

      I’m guessing your unit sits on the ceiling joists in the attic. You’ll need to figure out a way to tilt the unit to get the required 1/8″ slope. Examine the unit to determine if it’s fastened to the joists or just sitting there. Loosen the fasteners (if present), then slip some Strait-Flex Drywall Shims under the unit to obtain the proper tilt toward the condensate drain. Home Depot sells the Strait-Flex shims.

      The unit will be raised no more than 1/2 inch on one side, so there shouldn’t be any problem with disturbances to the duct work, electrical and plumbing connections.

  78. Shannon Colorado June 18, 2012 at 3:43 pm - Reply

    Thank you for this informational web page. I cleaned my coils and got my ac working with the information you provided. It is supposed to be 100 today so I really needed this help. Keep up the great work!

  79. Thomas July 6, 2012 at 9:53 am - Reply

    We recently noticed a puddle of water in our basement under our furnace and called a company to come in and check it out. They told us that the condensation pan attached to the evaporator coils was cracked, rusted and leaking with no way to fix. They suggested we replace the entire AC unit for somewhere between 6K-7K. Needless to say, I was shocked… actually horrified.

    He went on to explain (to me over the phone, as my wife was home that day) that these parts are not available anymore since the unit was 20 years old. When I got home, I took off the cover to expose the coils and the pan but could not find a leak anywhere. I could not get to the back of the unit and check for leaks back there as it is in a tight space in our basement.

    I guess my question is, can this be fixed and is the pan (if it really is leaking) replaceable by itself or is it one entire unit? The part number on this is G/UA048SA 4 ton coil (R22) on a York AC unit.

    any advice would be greatly appreciated.

    • Bob Jackson July 6, 2012 at 10:27 pm - Reply

      $6000.00 or more?! Now that’s scary, but you’re being taken for a ride. Recommend calling a York factory-certified service company. United Part Supply for $265.44 and it’s in stock. (Disclaimer: I am not endorsing United Part Supply, however their website has all the right customer satisfaction policies). At least you now know that:
      1) The drain pan is available as a repair / replacement part.
      2) The cost is not outrageous.

      Installation labor will be extra for the drain pan. Contact a York Certified Dealer for a quote. Get at least 3 quotes if possible. I’d purchase the drain pan from the local York dealer, you may pay extra (within reason) but it’s better to have the dealer be accountable for the entire repair and work guarantee.

      Write back and let me know how your repair turns out.

  80. Linda Ramirez July 7, 2012 at 1:50 pm - Reply

    My 5 year old TRANE 2 ton unit is acting up. The air is running constantly. I think its because its not (cooling) reaching its set temp of 76. The coolest it gets is 80 degrees. I’ve checked and cleaned the outside unit but still only 80 degrees. I don’t see freezing or anything…my husband and I are thinking that it may need an a-coil cleaning. What do you think? I’ve read ALL the posts, do you think its something we may be able to do ourselves?


    • Bob Jackson July 7, 2012 at 3:40 pm - Reply

      If the AC seasonal maintenance is up to date – air filter replaced, refrigerant charge and pressure OK, evaporator coils are clean, outside compressor coils are clean, the compressor fan is running, etc. – then the problem may be your 2 Ton AC system simply can’t keep up with the cooling demand of a 106 degree F day in the Kansas City area.

      Recommend calling an factory certified Trane HVAC service company to do a routine health check on your system. The service call will be around $100 and the HVAC tech can verify the system is OK and correctly sized for your home.

      Last week the temperature in my area of North Georgia was 104 degrees F – a new high temperature record. I have two 3 ton AC systems and two thermostats, one for upstairs and one for downstairs. Both AC systems ran non-stop all day and most of the night. The downstairs thermostat held at 75 degrees, while the upstairs thermostat read 80 degrees with a 75 degree set point. The upstairs cooling capacity couldn’t match the heat load until very late in the day.

      Assuming your 2 ton AC system health checks out OK but is unable to keep up with the very hot days, your options are:
      * Upgrade your AC system to increase the cooling capacity, however this is expensive.
      Decrease the heat flux coming into your home by:
      1. Add attic insulation to at least an R30 or better R60 rating. This will have the greatest impact dollar for dollar.
      2. Close the curtains and blinds to keep out the sun and infrared heat radiation.
      3. Buy a dehumidifier; drier air feels more comfortable.
      4. Ceiling fans to move the air.

      Also verify your attic is adequately ventilated. Attics are hot, but shouldn’t be any hotter than necessary. The U.S. Dept of Housing and Urban Development ( recommends “Attics will be ventilated with a minimum of 1 square foot of free vent for each 300 square feet of roof area.”. The attic ventilation can be a combination of power attic fans, roof turbines, ridge vents, box vents for outflow air with soffit and/or gable vents for inflow air.

      Please post back with what you decide to do.

  81. Kandy hair July 28, 2012 at 7:13 am - Reply

    My AC unit is not cooling as well as it should and I suspect my A-Frame coil is partially plugged with pet hair/dander that has been sucked up into the inside of the coil. I cannot access the inside of the A-frame without having the refrigerent drained and the A-frame removed. Is there any approved coil cleaning solution that will dissolve the hair and allow me to rinse it out down the drain tube? Any suggestions as to how to get the hair out without having to pay a professional to do it would be appreciated.

    • Bob Jackson July 28, 2012 at 5:47 pm - Reply

      Please see this new post explaining how to inspect the inside of the coils and give it heavy duty coil cleaning.

  82. Denise August 21, 2012 at 9:30 am - Reply

    Hi Bob,
    It has been a hot summer and we have been running the a/c non stop. I have noticed a foul smell all summer and couldn’t figure out where it was coming from. Last week it finally got cooler. I turned off a/c for four days. Yesterday the temp went back up and right after the a/c was turned on the odor returned. We turned off the a/c and just ran the fan and there was no smell. Does this mean the evaporator coils need to be cleaned? Could it be something else? HELP

    • Bob Jackson August 21, 2012 at 11:13 am - Reply

      Dirty evaporator coils are the most likely cause – algae/mildew growing on the coils will cause the sour or foul odor. The condensation drain pan should also be checked for standing water, algae and possibly a clogged drain line.

  83. Denise August 22, 2012 at 10:53 am - Reply

    Hi Bob,
    We looked inside at the evaporator coils and from what we can see they look clean (just like your photo’s). The drain pan looks normal too. Could it be built up on the inside? Should we use they coil cleaner spray foam anyway?
    We also replaced the drain line. Thanks for your help.

    • Bob Jackson August 23, 2012 at 4:49 am - Reply

      The algae and mildew could be on the inside of the coils or perhaps just along the bottom. It doesn’t take much to make an odor. Try the foaming cleaner first to see if helps with the odor, then you’ll know you’re on the right track. Spray a bit of the cleaner on the A-Frame cap in case water is pooling there.

  84. Debbie June 2, 2013 at 8:34 am - Reply

    Hi Bob, I live in a tropical place and AC is on 24/7. My unit is 7 years old and from initial installation I’ve had regular maintenance. 2 weeks ago the system stopped cooling, so our maintenance company added freon. 2 days ago the unit stopped cooling again so we shut it off all together at the advice of our tech.

    Yesterday, after he inspected the system he has recommended we replace the coil. And listed several other things he would have to replace as well. ( I’m not sure how he came to the conclusion that the coil was the only area leaking, except to say that he could hear and see freon leaking from it)

    My questions are:

    1 – because we’ve had the unit serviced regularly, and part of the service is cleaning the coil, would they not have noticed a growing problem with the coil during the service check

    2 – is it common to replace the entire handler when the coil is the problem ( we are being told that because the handler is in a bad location it is difficult to get to the coil

    3 – are there any particular questions I should ask to be sure the tech knows what he is talking about?

    4 – which brings me to my last question, if the coil is in a bad location to remove / exchange, how were they able to clean it. ( I’m willing to accept that they just spray it with something, but wanted your opinion)

    Thank you for your time.

    • BobJackson June 2, 2013 at 10:43 am - Reply

      > 1 – because we’ve had the unit serviced regularly, and part of the service is cleaning the coil,
      > would they not have noticed a growing problem with the coil during the service check
      Maybe, it depends on how fast the leak(s) were developing and the location. A refrigerant/oil leak on the interior the A-frame coil might not be visible. The refrigerant gas is invisible but since oil and water don’t mix, the oil can often be seen on the coils.

      > 2 – is it common to replace the entire handler when the coil is the problem ( we are being told
      > that because the handler is in a bad location it is difficult to get to the coil
      I believe it’s best to replace the entire air handler (electronics, blower motor, housing, etc.) when replacing the evaporator coils. The newer dual speed systems run more (on low speed) providing better comfort and humidity control. You’ll benefit from 8 or 10 years (or whatever the age of your old system was) technology and quality advancements with a comprehensive system warranty.

      > 3 – are there any particular questions I should ask to be sure the tech knows what he is talking about?
      Recommend getting a written statements on:
      * Itemized Statement of Work – exactly what work is to be done and new parts to be installed?
      * Warranty – parts and labor
      * Compatibility with your outside A/C compressor unit. Is the new air handler factory approved for use with your A/C compressor unit?
      * Your existing copper refrigerant lines will typically be reused. Were these inspected for interior/exterior corrosion and overall condition?
      * Did the HVAC technician inspect your A/C compressor? Because you live on a Caribbean island, salt corrosion, age of the unit and year-round duty cycle affect longevity.
      * Is your A/C system adequately sized for your home? No much you can do about this unless the outside compressor unit is also replaced. The evaporator coils / air handler much match the BTU tonnage rating for your compressor.
      * Do the new A-frame coils have a removable end plate to inspect and clean the interior side of the coils?

      See my comments dated December 27, 2012 at 12:58 am in Part 1 of the project about all-aluminum coils.

      > 4 – which brings me to my last question, if the coil is in a bad location to remove / exchange,
      > how were they able to clean it. ( I’m willing to accept that they just spray it with something,
      > but wanted your opinion)
      The technician most likely sprayed the coils with professional grade cleaning solution and a pump sprayer with a wand to get to the hard to reach places as I’ve shown in Part 3.

      It’s best to get three quotes from factory-authorized dealers to compare advice, terms and price.

  85. Debbie June 7, 2013 at 3:31 pm - Reply

    Thanks Bob, your response was extremely helpful. I’ve received 2 quotes so far, and expecting a third by tomorrow. Thanks again.

  86. Jack Allison June 30, 2013 at 3:35 pm - Reply

    Great website! Based on your “How to” procedures I plan to attack my 17 year old C14-41-1FF Lennox system to see if I can get to the evaporator coils to clean them. We’ve been in the house 10 years and I know the folks that had it for 4 years before us did not clean anything! The old Lennox has been problem free until last year when I replaced the condenser fan motor. It was cooling fine until this week (99-103 temps) when the ducts connected to the right side of the supply plenum started putting out 80 degree air, while the ducts connected to the left side are putting out 58 degree air. I replaced the Filtrete filter yesterday, as I have done every 2-3 months as they recommend. Doesn’t make sense to me, but thought it might be something you have experienced.

    • BobJackson June 30, 2013 at 5:02 pm - Reply

      > the ducts connected to the right side of the supply plenum started putting
      > out 80 degree air, while the ducts connected to the left side are
      > putting out 58 degree air.

      One side of the evaporator coils could be blocked, but I’m wondering if there might be a problem with the duct on the right side of the plenum.

      Is the air blowing much more strongly from the cold vents compared to the warm vents? Maybe the right side (80 degree air) of the plenum duct work is blocked? Look for an inline damper, collapsed duct or a separated duct connection if cleaning the coils doesn’t fix the problem.

  87. Jack Allison June 30, 2013 at 6:57 pm - Reply

    >Is the air blowing much more strongly from the cold vents compared to the warm vents

    Air flow is balanced – the same at all vents. Had one duct where a mouse had chewed his way in out near the dining room register and one that had partially separated from the plenum about 1/4 inch – fixed those 2 days ago. All other ducts seemed to be intact and dampers appear to be physically aligned as they have been since we moved in. Someone must have done a good balance job when the unit was installed. I’ll have to wait till tomorrow morning when the attic cools to get you a picture of the ducts coming out of the plenum. They actually come out of all 4 sides and the top. I’ll identify the ones that are providing cold air if that will help.

  88. Jack Allison July 2, 2013 at 9:12 am - Reply

    May have found the problem. After reading several posts I thought the evaporator coil might be iced up. Turned system off and and turned fan on to run constantly. Water is pouring out of drain. I did some drywall work in the house a couple of weeks ago and the dust must have plugged the ac filter more than it appeared. Will provide update if the new filter was the fix to the problem.

  89. Peter January 1, 2014 at 9:27 am - Reply

    Hi, have you used a product called ViperE+ ?

    I need to clean my evaporator coil and this is an option I can source locally. How good is it?

    • BobJackson January 1, 2014 at 10:29 am - Reply

      I’ve not tried that product. I read the manufacturer’s brochure and believe it will do a good job. Give it a try.

  90. Dalton April 4, 2014 at 12:15 pm - Reply


    This has been an invaluable help. I was quoted $1740 to inspect, clean and coat my existing evaporator coils. The units are 7 years old and we are experiencing “Dirty Sock Syndrome” of late. Thus I am hoping this cleaning procedure will alleviate the issue without having to spend nearly a third of the cost of the units themselves.

    Two questions:

    1. Would this sort of cleaning potentially address this issue?
    2. The price we were quoted, does that sound reasonable to you?

    Many Thanks!

    • Bob Jackson April 4, 2014 at 10:36 pm - Reply

      “quoted $1740 to inspect, clean and coat my existing evaporator coils” does strike me as expensive, but it depends on the HVAC service company’s work proposal. An AC system inspection will cost about $75 and cleaning in-place will run around $125 per unit; prices will vary by region, system configuration and other factors. Have you called another HVAC service company for a second opinion and quote? I wouldn’t mention what the first guy said to get their unbiased assessment.

      Is the AC service company planning to remove the evaporator coils? This requires draining the refrigerant, cutting the lines, pulling out the coils, cleaning, coating with protective spray, reinstall, connect the lines, evacuate the air and recharge the refrigerant. That amount of work would justify the $1740 price quote.

      Have your evaporator coils been cleaned before? How dirty are the coils? If the coils are caked with mold and sludge so badly that cleaning in place isn’t likely to be successful then pulling the coils may be reasonable for a thorough cleaning, but for $1740 I’d ask for a quote to install new coils. Back in 1999 I bought a house in Florida, discovered the evaporator coils had never been serviced and were a mess. I had the entire air handler replaced but the coils were leaking refrigerant and beyond repair. (Lesson Learned: Never buy a house without an HVAC inspection by a licensed technician.)

      “coat my existing evaporator coils” is interesting. Coating evaporator coils with a protective spray isn’t that common and requires access to both sides of the coils for the best coverage.

      While you might need an expensive system maintenance, I’d take a good look at the evaporator coils and if they’re not excessively dirty try a couple of in-place cleanings first. You can send photos to bob (at) if you’d like my opinion. Please include the make and model #.


  91. Dalton April 7, 2014 at 12:07 am - Reply


    Thank you again for your follow up. I followed your instructions and cleaned the evaporator coils as well as the condenser coils outside neither of which was terribly dirty. Yet I believe I did detect light mold infestation on the plastic drain pan under the Ev coils.

    I rinsed the pan with a bleach/water solution. Upon turning on the AC unit, we detected a moderate odour, musty in nature reminiscent of the original odour that led us down this path.

    Within 30 minutes of the AC running, we could no longer detect any odour. I welcome any of your thoughts on the matter.

    Thank you again,

    • Bob Jackson April 7, 2014 at 8:30 pm - Reply

      Hi Dalton,
      That’s great and you saved about $1700!

      The mold and/or algae growing in the drain pan was causing the dirty sock odor. It apparently took 30 minutes running for the system to air out.

      You might try drain pan tablets. These are inexpensive, work well and dissolve slowly to prevent mold and algae growth, odors and clogged condensate drains. Many home improvement stores have the product or you can order online.


  92. Joscelyn April 12, 2014 at 10:06 am - Reply

    I paid $118 to have this done with something lemon smelling. About 1 month later, the entire wall under the unit began to shake. We smelled burning under one vent nearby and turned unit off. Company came back out two days later, went up in attic, then came down and then turned on the unit. The company man could not recreate the noise. Really? It sounded like a helicopter landed on the roof just two days before? Unit was off for two days. Charged $50 for that little visit. Now, another two weeks later, our upstairs thermostat is malfunctioning. I have had a monthly contract with company for years. What is going on?

    • Bob Jackson April 12, 2014 at 11:40 am - Reply

      The problem is the blower motor in your attic air handler. The shaking wall, vibration, helicopter sound and burning smell was caused by either bad blower motor bearings or more likely a foreign object was sucked into the blower fan wheel. A piece of insulation, flex duct liner, HVAC tape or a portion of the air filter tore loose and got caught inside the squirrel cage blower wheel. This caused the roaring sound, vibration, overheating and burning smell. One reader had a similar problem:

      My wife put a dryer sheet in the filter when she changed it (to make it smell better), only problem is she put it on the wrong side and it got sucked into the system… It just started yesterday, sounds and feels like a helicopter hovering over my house every time the A/C turns on.

      Whatever was obstructing the blower motor is still inside your air handler. Since the vibration and noise has stopped, it’s probably been blown downstream and is now stuck against the heat exchanger or evaporator coils. Call the HVAC tech and ask them to open the air handler to look inside and remove the foreign object(s). It’s a problem waiting to happen and could result in a fire if the heating is turned on or will cause your evaporator coils to ice up due to air flow blockage. When the foreign object is removed, you’ll be able to identify it, figure out where it came from and fix the root cause so it doesn’t happen again.

      The HVAC tech should also check the blower motor bearings and current draw (Amps). The blower motor should rotate quietly and smoothly. The fan wheel should not be blocked with dust/dirt. A clamp meter on the blower motor power wires with the motor running will display the current draw in Amps. Excessive current draw above the motor rated current indicates the motor is wearing out and pulling more current. The HVAC tech can tell you when the motor needs to be replaced. Be sure the check the motor capacitor and replace that (it’s inexpensive) if needed.

      Let me know what you find.


  93. John Swift May 21, 2014 at 5:10 pm - Reply

    Is it really safe to use this foam stuff on the a coil that air in your home is going to blow over? It seems like it was designed for window units.

    Also, if you check the MSDS – it says not to mix it with oxidizers which if I’m not mistaken, bleach is one heck of an oxidizer.

    • Bob Jackson May 21, 2014 at 6:30 pm - Reply

      Hi John,
      Your concerns are valid and no manufacturer or their product liability legal staff would say it’s OK to use the two products together.

      I’ve used the “Frost King Foaming Air Conditioning Coil Cleaner” which has been replaced by the “AC-Safe Air Conditioner Coil Foaming Cleaner” several times on my indoor evaporator coils with very good results and no ill effects as have other people. The Material Safety Data Sheet (MSDS) for nearly any chemical product lists every conceivable hazard including “Avoid contact with strong oxidizers, reducers, acids, and alkalis.”

      Household bleach is a 5% to 10% concentration of sodium hypochlorite and a strong oxidizer in concentrations greater than 40%. After diluting the bleach 50/50 with water to rinse out the condensate drain line the sodium hypochlorite (bleach) concentration is only 2.5% to 5%.

      I also wrote in the project:

      Nu-Calgon Evap Foam no-rinse coil cleaner is specifically formulated for cleaning air handler evaporator coils and approved for use in and around food processing areas.

      which has an MSDS that lists similar hazards as the Thermwell AC-Safe foaming cleaner that you cited.

      In summary:
      * If you’re in a hurry then buy the off-the-shelf product at the home improvement store.
      * Order the specialty Nu-Calgon product online if you can wait a few days for shipping.
      * 50/50 diluted bleach and water isn’t considered a strong oxidation hazard.

      As always follow the manufacturer’s instructions and use in a well ventilated area.

      Thanks for asking,

      • John Swift May 21, 2014 at 7:34 pm - Reply

        Thanks for the feedback, I really do appreciate it. I used the cleaner on my coil this noon (I didn’t use the bleach for the pan though) – then found the MSDS online and started to panic. Thank you for putting my mind to ease.

        It does seem to work. Although, I’m not sure I’d use bleach in the pan at all when applying the foam product. To each’s own though. :-)

        Thanks for the informative post and thank you for getting back to me so quickly :-)

        • Bob Jackson May 21, 2014 at 8:32 pm - Reply

          Better to ask than worry!

          Per your concerns you could pour plain water down the drain line first followed by the 50/50 bleach and water solution or drop in the time-release drain pan tablets.

          It’s not a good day if you need a Mighty Pump™ A/C Condensate Drain Line Pump. I’ve seen drain lines clogged with algae, bugs, rust, sawdust etc. cleared with a Mighty Pump.


  94. Cris August 2, 2014 at 3:41 pm - Reply

    is it okay to open the backside instead on the front to clean the evaporator coil ?

    • Bob Jackson August 2, 2014 at 6:13 pm - Reply

      Opening the rear of the coil case is fine if you can. It’s not common because most coil cases only have a front access panel.

  95. Chris September 4, 2014 at 9:04 pm - Reply

    Just had maintenance come out and check our A/C unit because it started leaking all over the ground and seeping through the ceiling. They told and showed me that the A/C hadn’t been regularly maintained for quite some time and there was a bunch of build-up on the unit. They took some A/C coil cleaner and some water and sprayed it down with cleaner and then rinsed it with water. They said they’re going to eventually have to replace the condenser(or something) because it was in such poor condition. My question is, is it safe to run the A/C after they sprayed all those chemicals on it? Will they seep through my ventilation and pump into the rest of my house? I’m tempted to leave it off all night, but it is August in Florida and it’s hot. Thanks.

    • Bob Jackson September 4, 2014 at 10:03 pm - Reply

      If the “maintenance” people used a coil cleaner approved for evaporator coils then it’s fine to turn on the A/C immediately after the cleaning. The odor should be minimal, if any after a short time. If there is an odor that bothers you open the windows for a while and let the place air out, but I’ve never had a problem. Ask the maintenance which product they used and look it up online to be confident.

  96. Rudina September 5, 2014 at 9:50 am - Reply

    Hi Bob,

    I have a problem with coils they seem clogged up with a sheet of wet dirt and when the a/c is on ice forms on them. Last night the a/c didn’t cool down as it should, kept the temp at 79 although it was set for much lower. We live in Tampa, Fl so it is very humid and hot with no a/c. The problem is that my unit is upstairs and I can only access the coils from the bottom, how do I use the spray without spraying it on me and will it stay on or just drip over without cleaning the coils. Can I use a vacuum do clean the dirt? The unit is a Carrier, it appears old I’m not sure how old, since I am renting the house I don’t know. But I am responsible for maintaining the a/c unit under contract. Please help! Thank you!

    • Bob Jackson September 5, 2014 at 1:36 pm - Reply

      Hi Rudina,
      That “sheet of wet dirt” is blocking the air flow and causing the evaporator coils to get so cold they’re icing up, making the problem worse.

      You might be successful vacuuming the coils with a wet/dry shop-vac. Take care to use a very soft brush attachment to avoid bending delicate coil fins. A regular vacuum cleaner isn’t suitable unless the coils and caked on dirt is completely dry. Part of the problem with just vacuuming the coils is it won’t disinfect the coils. I suspect there’s mold and algae growing in that sheet of wet dirt.

      > how do I use the spray without spraying it on me…?
      A better way to clean heavy dirt is shown in AC Evaporator Coil Cleaning with Pump Sprayer and Brush, the difference for your situation is to use the bench brush on the area of the coils that you can reach from the bottom.

      > …and will it stay on or just drip over without cleaning the coils?
      The cleaning spray should stick to the coils and wick down to the condensate drain pan.

      Do you see a model # on your Carrier unit? You can send photos of the air handler to bob (at) for more specific advice. Replace the (at) with the @ sign.


  97. Carrie September 19, 2014 at 10:41 pm - Reply

    Thanks for this article! I have one coil (like \ instead of /\) that’s dripping. The water is clearly supposed to run down the angled surface to the drain, but instead it drips straight down off the surface. I followed this article and applied some foaming coil cleaner. It quit dripping for about a week after that, and drained properly into the drain line — but then it started dripping again.

    I’m at a loss. Does it need deeper cleaning? If so, why did the foaming cleaner stop the drip for a week? Is dirt building back up that fast? I’m curious if it’s something I could fix myself or if I should just steel myself to pay to have it serviced.

    • Bob Jackson September 20, 2014 at 8:48 am - Reply

      Hi Carrie,
      Your air handler has a “slant coil” configuration similar to this Goodman model.

      The condensate water should wick down the coil into the condensate drain pan instead of dripping off. The problem is the coils are “hairy” from dirt/mold that acts like miniature stalactites.

      > If so, why did the foaming cleaner stop the drip for a week?
      > Is dirt building back up that fast?
      The foaming spray cleaner is good for lightly soiled coils and temporarily knocked down the mold. After a week or so the mold reestablishes and the coils are hairy again. Mold can grow very fast with favorable conditions. Examine the coils with a magnifying glass and flashlight. What do you see?

      Also check the air filter for damage, proper fit and replace it if needed.

      > Does it need deeper cleaning?
      Both sides of the evaporator coils need cleaning and disinfecting. See AC Evaporator Coil Cleaning with Pump Sprayer and Brush for details.


  98. Rosie September 21, 2014 at 12:32 am - Reply

    Hi Bob,

    I have a continuous foul smell coming from my school air conditioner. After they clean it, the odor returns after 3 weeks. During those 3 weeks, my students eyes get irritated, they cough and gag. Please give me some advice.

    • Bob Jackson September 21, 2014 at 4:01 pm - Reply

      Hi Rosie,
      Is this a central air conditioner system or a window mounted unit?

      The foul odor could be originating from several sources:
      * Dirty / moldy evaporator coils.
      * Mold and algae in the condensate drain pan.
      * Clogged condensate drain tube causing.
      * Mold inside evaporator coil case (cabinet) and insulation.

      If your unit is that smelly it should be fairly simple for the maintenance personnel to identify the source of the odor.

      How are they cleaning the evaporator coils? A thorough cleaning on both sides of the evaporator coil is necessary to remove all the dirt and disinfect the coils to prevent mold and algae growth. I also spray the inside of my evaporator coil case with Lysol after cleaning to disinfect the cabinet insulation and plenum surfaces.

      Drain pan tablets will prevent mold/algae and keep the drain line flowing. The tablets dissolve slowly over many weeks.


  99. Nikola October 4, 2014 at 10:14 pm - Reply

    I have been told that my evaporator coils need to be cut out and cleaned with an acid bath for $610. I am terribly frustrated with this (and with other aspects of the service I have been receiving). Unfortunately, my house is very hard to keep clean, with 4 cats and 2 large dogs that track in a lot of dirt from the sandy backyard. I have been told repeatedly that if I change the filter frequently enough dirty coils won’t be a problem but I am certain there is air bypassing the filter. I have resorted to adding weather stripping and foam strips to stuff around the perimeter of the filter and am looking into a more sturdy reusable filter frame.

    The coils are quite dirty but the entire system is only 2 years old (still paying for it) and I have had cleaning done on the previous handler with the coils in place out, so I am reluctant to jump straight to the 600$ solution. I am waiting for a shipment to come with a pump sprayer and cleaning solution that you recommend in your heavy duty cleaning tutorial.

    Is it likely I will be able to clean it well enough myself? How will I know if I have done an adequate job or if it is beyond saving? Should I defer to the word of a professional? Should I get a second opinion?

    • Bob Jackson October 5, 2014 at 10:14 am - Reply

      Hi Nikola,
      Are your return air vents located on or near the floor where pet hair and dust can be drawn into the system? Having cats and dogs in the house shouldn’t be causing the problems you’re seeing with excessively dirty coils if the ductwork is sealed and the air filter changed regularly.

      You might try placing vent filter covers on the return air vents that you suspect are pulling a lot of dirt:

      You’ll know before long which return vents are pulling in the most dirt and if that the source of the problem.

      > I have been told repeatedly that if I change the filter frequently enough dirty coils
      > won’t be a problem but I am certain there is air bypassing the filter.
      Has anyone inspected your ductwork, return air plenum and the filter slot for open joints and proper fit? I think you’re on the right track that air is bypassing the filter. Weather stripping shouldn’t be necessary because the filter frame is pressed against the plenum filter slot when the AC is running to minimize air leakage.

      > Is it likely I will be able to clean it well enough myself?
      Yes if you’re careful and patient.

      > How will I know if I have done an adequate job or if it is beyond saving?
      The AC service company wants $600 to remove the coils to clean both the inside and outside surfaces. See How to Clean Inside of AC Evaporator Coils for how to do it without removing the coils. This technique assumes the coil cover plate can be removed. You’ll know if the coils are clean because you can inspect the inside and outside of the coils. Shine a flashlight through the coils onto a mirror to verify the spaces between the coil fins are clear of dirt and debris.

      > Should I defer to the word of a professional? Should I get a second opinion?
      Ask your AC service company if they can clean the coils in place by removing that front cover plate. It’ll avoid the cost of cutting the refrigerant lines and recharging the system. Again, it depends on your coil configuration if the cover plate can be removed.

      Good luck!

  100. David March 3, 2015 at 9:58 am - Reply

    Hi Bob,

    I recently had my A-Frame coils cleaned (coils were really dirty, 5yrs w/o cleaning) & after realizing how much I paid, I’ve decided to be a bit more proactive with the up keep. I plan on getting the Nu-Calgon spray as I’ve seen many other techs using it in their videos. My question to you is do you only spray the cleaner on the outside coils or do you also spray on the inside too? My concern is that if I spray it on the inside of the frame, some of the foam will drip on the filter below. Any help/pointers is greatly appreciated.

    • Bob Jackson March 3, 2015 at 8:06 pm - Reply

      Typically the cleaner is applied to the exterior side of the A-Frame evaporator coils because those surfaces are exposed when the coil case panel is removed. On some coils it’s possible to remove the endplate to clean the inside as explained in How to Clean Inside of AC Evaporator Coils.

  101. crystal le May 9, 2015 at 4:57 pm - Reply

    i wish I found your article earlier. I called a company for duct and dryer cleaning (known company). the technician checked my heating system (15 years old with no problem) saying that the ac coil is rusting. It is still good since the rust is only 1/8 of an inch. Otherwise it could be a costly repair as each system cost around 12 K for systems down the line. He said even if he cleans the duct, it would be a waste of money, instead, he suggested to install 2 uv lights (the speedlight Jr), one in the return and one in the supply. He will clean the ac coil, the heat exchanger, blower and spray with 2 bottles of foam. He said he will try to clean the loosen rust. He said the uv light will dry the system and avoid further rust and extend the life of these 2 furnaces. He also cleans the duct, dryer for me. He said the uv light is lifetime guarantee and he will come back every year to change the bulb while the AC coil is 5 year warranty. He charges me $2,700. I agreed to it but I think I did it hastily. What do you think? Is it reasonable for the job? the rust is no where close to the picture shown.

    • Bob Jackson May 10, 2015 at 12:58 pm - Reply

      Rusty evaporator coil end plates are normal, especially for a 15 yr old system. The end plates simply brace the coils and prevent the airflow from spilling out the ends. If there are no holes then ignore the rust.

      I spent $931 for spring maintenance last year. So yeah it gets expensive and $2700 doesn’t seem excessive for cleaning the evaporator coil, condenser coil, install two UV lights with annual bulb replacement and dryer duct cleaning. The best way to determine what’s a reasonable price is to get 3 estimates from reputable contractors who have been in business for years. Take care to compare “like for like” services, materials and warranties.

  102. Shannon July 16, 2015 at 9:10 am - Reply

    I’m so thankful for sites like this that help inform homeowners so we don’t feel so uneducated when speaking to HVAC professionals. I know close to nothing about A/C units but recently had our unit serviced (preventative maintenance) for the first time since we purchased our home less than 2 years ago (yes, I know we should have been doing it 2x per year). The previous owners had multiple pets and used a cheap “reusable” filter on the indoor unit. We have been very good about changing the air filter regularly and the unit is only about 4 years old so we didn’t expect any issues. However, the gentleman servicing the unit said our evaporator coil was extremely dirty. After taking a look for myself, I was completely disgusted with all the dirt, pet hair and grime on the coil. Our unit allows fairly easy access to the coil by just removing the air filter as the coil sits at the bottom of the unit. It’s tight but we are able to get in there. The A/C tech quoted us something in the range of $700 to have the coil cleaned (mentioning an “acid wash” needed which I’ve been unable to find any information on online). We researched cleaning indoor coils online and decided to try for ourselves using the foaming cleaner. We were able to remove quite a bit of junk from the coil with just the cleanser and a toothbrush (making sure to brush along the grain of the coil as to not damage the fins) but there seems to be sand-like granules in between the fins. Is there another way to get this out or would another try with the foaming cleanser possibly work? I guess we are just interested in trying anything possible before having to pay so much for a fairly new unit. Thanks so much!

    • Bob Jackson July 16, 2015 at 9:09 pm - Reply

      Always hire an HVAC tech and a roofer before buying a new house. Home inspectors aren’t prepared or equipped to open up the air handler, check the coils, electrical and gas pressure. My last home inspector wouldn’t walk the high and steep roof, otherwise I’d known about the defective and crumbling Atlas Chalet shingle. Or my prior home with an AC system that had never been serviced and was completely clogged and moldy. It would’ve saved me thousands upon thousands of dollars. Also don’t accept the home inspector(s) recommended by the realtor due to conflict of interest. The realtor wants a fast trouble-free sale and easy inspector.

      If your home has a wood deck hire a deck company to inspect it for problems. More often than not decks need expensive repairs especially if it’s 8 or 10 years old.

      > Is there another way to get this out or would another try
      > with the foaming cleanser possibly work?
      Foaming cleaner and toothbrush has probably done all it can. The dirt between the fins will need to be washed out with a pump sprayer. See these projects:
      Heavy Duty AC Evaporator Coil Cleaning
      How to Clean Inside of AC Evaporator Coils

  103. amani guillaume January 13, 2016 at 3:05 pm - Reply

    helo, i’m amani. i have cleaned the AC evaporator of a standing split with soap and water. now it show error 6 and stops runing after a few time. please help me to resolve this problem. i specify that the manufacturer is midea and the model references are: split type air conditioner , model MFS3-48CR. Thanks so much.

    • Bob Jackson January 13, 2016 at 6:20 pm - Reply

      I can’t find information on the Midea mini-split air conditioner model AC-MFS3-48CR, however error code E6 on related models indicates it’s a temperature sensor problem.

  104. Franklin Copeland June 20, 2016 at 4:53 pm - Reply

    Is this the same as a down flow coil

    • Bob Jackson June 20, 2016 at 9:27 pm - Reply

      My air handler is the upflow type – the blower motor is below the evaporator coils. The A-frame evaporator coils are the vertical style which can be used in either an upflow or downflow air handler. Note that vertical air handlers sit upright like filing cabinet. Vertical coils have the condensate drip pan at the bottom of the A for both upflow and downflow applications.

      A-frame coils are also used in horizontal air handlers (the air handler lays on it’s side) however the condensate drip pan is located on the side of the A as shown in this Goodman horizontal coil and horizontal coil installation instructions.

  105. mike l July 23, 2016 at 2:45 pm - Reply

    I have a 14 yr old a/c system, had the hvac company out and they say it needs a new ev coil,the water is not draining out the drain line but is draining out the overflow line, they cleaned the main drain line. This is a 4 ton unit, I live in Houston,tx so plenty of heat and humidity. should the coil be replaced? they quoted me 1919.00 for everything. thank you for your time it is also still not draining out the main line,most of water is still coming out of overflow pipe

    • Bob Jackson July 23, 2016 at 7:07 pm - Reply

      Did the AC company say exactly why the evaporator coils need to be replaced? Why is the condensate water not draining properly? Do you have a metal condensate drain pan that has rusted through? It may be possible to replace the only the drain pan but it depends on the coil and refrigerant line arrangement, horizontal versus upright coil configuration, etc. If the lines have to be cut to pull out the coils before replacing the pan, it may be more cost effective to replace coils.

  106. Andrew July 25, 2016 at 6:09 pm - Reply

    not sure how to clean at Lennox G43UF series coils.

    • Bob Jackson July 26, 2016 at 1:02 pm - Reply

      G43UF is the model # of the Lennox gas furnace. The evaporator coil model # should be on the coil case that sits on top of the furnace cabinet.

  107. Jan August 27, 2016 at 10:05 pm - Reply

    My A/C coils in the air handler needs cleaning. They are not as dirty as some pictures of dirty coils. Must of the build up is on the corner sides and around the bottom. There is no issues concerning having a proper air flow etc. I just want to have it cleaned. My A/C unit is a Trane, put in 2008 when my townhouse was being built. I purchased it in the same year…in December. My unit is upstairs on the second floor. My question to you can my A/C coils be cleaned in place in the A/C air handler?

    • Bob Jackson August 28, 2016 at 11:56 am - Reply

      If you can see the dirt it can be cleaned.

      Realize most of the dirt will be inside the coils on the upwind side. Some coils like mine have a removeable endplate to access and clean inside. Other models like the Rheem RCBA product line are so boxed in the coils have to be cut out and removed for cleaning or replacing.

  108. Thomas Motley October 2, 2016 at 7:03 am - Reply

    Hi, thanks for the article. in the first photo of Part 1, you label an air filter where the incoming air meets the furnace. I assume the filter that you recommended changing once a month is not that one–but rather the kind in the interior wall of a house–but is the labeled filter something that needs to be changed at all?
    Also, you mention a couple different types of foam cleaner. The AC-Safe stuff is about 1/4 the price. Were you recommending the Evap Foam mainly for use in and around food processing area? Not surprisingly, I don’t want to spend anymore than I have to.
    Also, I was reading a Q&A about a similar project, and after seeing the photos of the guy asking for help, someone said, “You have a 90+ furnace, which means most dirt would not get to the A coil because the heat exchanger for the furnace would catch it first.” I’m not sure whether you have a 90+ furnace, but doesn’t the air go through heat exchanger before it hits your evaporator coils? Is that guy full of it?
    Finally, I also read about evaporators that have no access panel. Some recommended not touching it, others suggested getting an HVAC professional to deal with it, and still others suggested cutting out a panel in the sheet metal. What’s your advice? Thanks again.

    • Bob Jackson October 2, 2016 at 12:01 pm - Reply

      I’ve not tried that other brand of coil cleaner. If saving $10 or $20 on coil cleaner makes sense when servicing your $10,000 central A/C system, I have no further comment.

      That guy on DSL reports you referenced is wrong on so many points. See AC Evaporator Coil Cleaning with Pump Sprayer and Brush.

      > I also read about evaporators that have no access panel.
      Have you opened your access panel to look at your configuration? I prefer to give specific advice versus what if’s.

      There are a variety of evaporator coils that can’t be serviced in place by removing the endplate. These are often the W, double A or triple A coil configurations. Sometimes there are too many capillary tubes in the way or the endplates are welded. The refrigerant lines have to be cut to remove the coils for cleaning. Often it’s just as well to replace the coils. For example, this Rheem/Ruud RCBA coil can’t be cleaned in place and has to be cut out.

  109. jon November 2, 2016 at 11:29 am - Reply

    Good Article.. I bought a home with 20year old a/c units. they are still in good working condition. rather than replacing them, I purchased a home warranty along with having an a/c company do regular maintenance on them. I have two ac units. I recently noticed a leak in my kitchen ceiling. my ac unit in the attic is similar to what you have described. I had a plumber tell me that the leak was coming from the condensation pipe, and he also told me my drain pan was full of rusty water and clogged. my a/c guy was out four months ago for regular cleaning/maintenance. I had him out again to tell him of the problem. he said the pipe is not clogged but the air handler floor was full of water, the primary pan was cracked, and the evaporator coils were rusting and chipping off. and that this is not repairable but needs to be replaced. he said the system already had a water safety switch on drain line prior to use of this specific a/c ompany. they are now quoting me 3100 to replace all plus refrigerant. this does not even take care of my $400 leak detection test from plumber or the reaplcement of ceiling in kitchen damage from the water leak. currently there is no water coming out so must have been old/ a while ago….

    I guess my question is, can this happen. he did a coil cleaning on june1, they can go bad that fast? or go from cleaning, no issues to now replacement and 3100$ job? doesn’t make sense. the warranty company will not cover any of this

    • Bob Jackson November 2, 2016 at 8:47 pm - Reply

      It’s just coincidence the drain pan wasn’t leaking 5 months ago. The steel end plates always rust but it’s cosmetic so long as the coils aren’t leaking refrigerant.

      Replacement evaporator coil drain pans are available from several sources, for example:

      The freon will have to be drained and the copper supply & return tubes cut to remove the old coils to replace the drain pan. Then the tubes will have to brazed and the refrigerant recharged. Whether or not it’s cost effective depends on the price of the new coils and how confident you are in the remaining longevity of your old coils.

      Ask for quotes from two other HVAC service companies to compare options, prices and warranties. If you decide to keep the old coils have them thoroughly cleaned inside & out while they’re out of the air handler.

  110. Russ November 30, 2016 at 2:32 pm - Reply

    Hi Bob,

    My Rheem AC unit has no drip tray. Each evaporator section has a tiny tray at the bottom, tied to each other and the drain line at one end. I can’t seem to get it to flow properly. Any ideas?

    • Bob Jackson December 1, 2016 at 4:42 pm - Reply

      Sounds like the condensate drip tray is just wide enough for the bottom edge of the evaporator coils to rest inside. The tray may be clogged due to dirt/gunk on the bottom of the coil fins. Try cleaning the tray and fins with a pump sprayer.

      It’s often possible to slightly raise the coils because they just sit on the condensate tray. 1/8 to 1/4 inch lift would be enough to rinse underneath the coils.

      Also see How to Clean Inside of AC Evaporator Coils.

  111. David Diepenbrock December 16, 2016 at 10:36 pm - Reply

    Much thanks for all your instructions here Bob! We’ve lived in our house only a bit over 2 years. I hired a company last winter to service my furnace and as I watched they hardly did anything but vacuum what was easily accessible. Not being very impressed I decided I would learn a few things for myself, and your site is perfect.

    I had a similar problem to Tim, where there was no access to the evaporator coils and your instructions for cutting an access panel worked great. I held up a shop vac to the drill as I made the pilot hole to try to minimize any shards getting inside and it seemed to help some. It looks like the installers just didn’t make any way at all to clean the evaporator coils, the whole thing is enclosed in sheet metal with no openings at all (upflow A-frame unit). The unit is in the basement inside the envelope so there’s no insulation on that sheet metal either, I suppose that’s okay.

    A week ago I took apart the blower wheel to clean it, and it was filthy (I suspect the previous owner never cleaned anything on the furnace). Its probably made worse because the unit only had an electronic air cleaner which doesn’t seem to do quite as good of a job of catching dust. Because of how dirty the blower was I expected the evaporator coils to be pretty dirty too, but all I found was a few pieces of dust which I was able to easily grab with the shop vac without even touching the fins. The furnace is about 13 years old, and from the looks of the compressor outside it’s probably about that old too. I’m a bit stumped, is it normal to replace just the evaporator coils?

    I started all this work because it seems like the furnace is having to work harder than it ought to heat the house. I’ve gone through various phases of cleaning and checking. Gas pressure is in check, return ducts are pretty clean (there’s just 2 central returns) but I’m was seeing over a 100 degree temperature rise (return air vs. supply in the plenum), the furnace spec says it should be 60-80. The other thing beside cleaning I’ve done is move the blower to high speed for the furnace which dropped it to about a 90-95 degree rise, so I’m still looking for what more I can do to get that number down and improve the efficiency and lifetime of the furnace.

    • Bob Jackson December 17, 2016 at 11:42 am - Reply

      In a nutshell your situation is:
      * 13 year old air handler
      * Upflow system like mine: blower at the bottom, furnace in the middle, evaporator coils on top.
      * Air flow seems constricted due to the abnormally high air temperature rise across the furnace.
      * Filthy blower wheel.
      * The evaporator coil case lacked an access panel until you made one.
      * The top/downwind face of the evaporator coils appear to be reasonably dirt free.

      Have you checked if the upwind/interior coil face is dirt free? Given the filthy blower wheel, age of the system and the coils have not been routinely cleaned this may be the problem.

      Try the flashlight and mirror technique if possible to check if the interior coil face is clogged. If so, you may have to cut a large access panel to remove the A-frame coil end plate to clean inside the coils.

      • David Diepenbrock December 22, 2016 at 9:33 pm - Reply


        Thanks for your quick response!
        I cut a large access panel and removed the A-frame coil end plate — which is not as easy as it sounds, because there’s all sorts of small copper pipes running in front of it. The inside was not dirty at all. With how dirty the blower wheel was, this almost certainly was replaced not so long ago. For the moment (and because I was short on time to get the furnace put back together) I left the end plate off since it seems that air escaping out the side of the A-frame won’t hurt during the heating season, although I doubt that really matters much. I didn’t get to clean it this go around, but will definitely do that after the holidays.

        I did some measuring of my supply and returns, and found there to be a choke point just after the first bend in the return. The return through the air filter and into the furnace was a 26×16 duct, but it took a bend upward into a 26×10 duct. I measured out the supply side, which split immediately for the two levels, and the combined area of the supplies was larger than that of the return. So I added another return in the basement going into the 26×16 part of the duct so that now my total return area is just a bit larger than the supply area.

        The combination of the added return and removing the end plate leaves the temperature rise is now down to between 70-75 degrees, so I’m within spec now. I’m perplexed by the lack of access to the evaporator coils, and that the installers didn’t seem to ensure adequate airflow. I know my quick “hack” of a fix isn’t an ideal solution, but it should at least help keep the furnace from overheating.

        • Bob Jackson December 23, 2016 at 1:17 pm - Reply

          Sorry you had to go through all that trouble to isolate the problem to the too small return duct.

          > I left the end plate off since it seems that air escaping
          > out the side of the A-frame won’t hurt during the heating season
          The end plate doesn’t matter during heating but it must be installed for cooling. Otherwise the air will spill out the end of the A-frame coils instead of passing through the fins.

          > The return through the air filter and into the furnace was a 26×16 duct,
          > but it took a bend upward into a 26×10 duct.
          A 26×16 inch duct has 416 square inches of area versus only 260 sq. in. for a 26×10 duct. That’s 37.5% smaller and definitely a choke point on the return air plenum.

          > I’m perplexed by the lack of access to the evaporator coils, and
          > that the installers didn’t seem to ensure adequate airflow.
          Likely a combination of low cost parts, air duct design error (assuming there was design) and/or installer supervision.

  112. Gilbert January 5, 2017 at 4:13 pm - Reply


    When it is hot outside, lets say 85 or above and the A/C is running, there seems to be a sewer like smell throughout the house. Now I know you might say, sewer is a plumbing issue, call a plumber.
    I have had everything plumbing related done to my house. No broken lines, no hairline cracks, no broken seals, etc have been discovered. Cameras were run through the sewer line, even smoke has been run through the pipes. Nada…
    The smell is only when the A/C is running on a hot day. I have poured bleach/water combo in the condensor drain and it of course smells like bleach in the house. The coils on the fan unit outside are clean. I am wondering if you could possibly think if the furnace coils could be causing this foul odor? I have not cleaned them yet because I know it is a tough task. But I will do it soon. I just wanted your thoughts and possible solutions.
    Thank you

    • Bob Jackson January 5, 2017 at 8:17 pm - Reply

      > The smell is only when the A/C is running on a hot day.
      So the odor is noticeable when the A/C is running more or less continuously.

      Most people describe dirty moldy evaporator coils as smelling like sweaty gym socks. Sewer gas has a very different distinctive odor.

      Sewer Gas Intrusion:
      Is the evaporator coil condensate drain line connected to the sewer plumbing? Is there a P-trap on the drain line? If “yes” to either question, it could be the P-trap is either missing or defective allowing sewer gas to be drawn into the air handler. The longer the A/C runs the more sewer gas is pulled into the house until you notice the odor. See Let’s Concentrate on Condensate by ASHI Reporter. See the 4th paragraph before the end of the article about sewer connections.

      Also see How to Clean Inside of AC Evaporator Coils if you believe it’s a dirty coil issue.

  113. Rick July 9, 2017 at 5:41 pm - Reply

    thank you. very informative in regard to cleaning. But I am wondering how to defrost the coils she they get iced up and of course how to prevent it from happening again.

    • Bob Jackson July 10, 2017 at 5:19 pm - Reply

      Ice on the evaporator coils usually means the refrigerant charge is low and indicates there a leak in system. You’ll need an HVAC service tech to inspect it. He’ll hook-up a set of gauges to check the high and low side pressures which is proportional to the refrigerant charge.

      My 17 old Heil central AC system needed to be topped off once a year the past several seasons because it had a slow leak. Usually about 1 lb of R-22 which is 20% of the total system charge. Leaking evaporator coils are the most common problem. The coils expand and contract slightly with every running cycle. Eventually one of the many brazed joints develops a leak.

  114. Kristie July 28, 2018 at 2:09 pm - Reply

    Do I spray the cleaner on while my ac is running?

    • Bob Jackson July 29, 2018 at 9:57 am - Reply

      That was covered in the project introduction:

      Before you begin, turn off the air conditioner at the thermostat and shutoff the electricity to the air handler. There should be a toggle switch (it will look like a light switch) by the air handler to turn off the power. If not then shutoff the electricity at the circuit breaker panel.

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