Heavy Duty AC Evaporator Coil Cleaning

By |Last updated on |Central AC Maintenance|61 Comments

Heavy duty AC evaporator coil cleaning with a pump sprayer and commercial cleaning detergent used by the pros. This series is continued from How to Clean AC Evaporator Coils – Part 2.

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
  3. Heavy Duty AC Evaporator Coil Cleaning (this project)
    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.

A-Frame Evaporator Coil Inspection

Homeowners are often concerned the interior (or upwind side) of the air conditioner A-Frame evaporator coils that are hidden from view may be clogged with mold, algae, dirt, pet hair and other debris that gets past the air filter. The problem is the A-frame evaporator coils are sealed on both ends by the metal support plates preventing access to the interior of the A-Frame coils. Inspecting and cleaning the interior of the A-Frame coils can be a challenge, especially if you suspect the coils are very dirty. Dirty evaporator coils will restrict the system air flow, even when heating in the colder months because hot air from the furnace pass through the evaporator coils.

My central air conditioner air handler in the attic is an “updraft” model (air enters from the bottom right and exits the top) and consists of a natural gas furnace on the bottom with the A-Frame evaporator coils on the top:

Cleaning Central Air Conditioner A-Frame Evaporator Coils

Cleaning Central Air Conditioner A-Frame Evaporator Coils

One may think it should be possible to view the interior of the A-Frame AC evaporator coils by opening up the gas furnace section, which looks like the following image for my unit. The heat exchangers are arrayed at the top of furnace cabinet – the air conditioner evaporator coils sits on top of the furnace, immediately above the heat exchangers:

Gas Furnace Cabinet and Heat Exchanger

Gas Furnace Cabinet and Heat Exchanger

An idea is to remove the inducer blower motor (orange) to look up through the heat exchanger array to the A-Frame coils. This strategy will not work because the heater exchangers are sealed by the blue and green metal baffles, blocking the view of the A-Frame coils:

Upflow Natural Gas Furnace Parts Diagram

Upflow Natural Gas Furnace Parts Diagram

A-Frame Evaporator Coil Inspection

An easy way to inspect the interior of the air conditioner A-Frame evaporator coils with a high intensity flashlight. No complicated disassembly required!

I’m shining my flashlight through the evaporator coils. It’s apparent the exterior surface of the coils are shiny and clean, but what inside the coils?

A-Frame Evaporator Coil Inspection with a Flashlight

A-Frame Evaporator Coil Inspection with a Flashlight

I can tell that the inside of the A-Frame evaporator coils are indeed clean because the high intensity flashlight shines brightly through to the far side, reflecting off the foil-faced insulation on the far side of the evaporator coil case:

Air Conditioner Interior A-Frame Evaporator Coil Inspection

Air Conditioner Interior A-Frame Evaporator Coil Inspection

Full view of the flashlight on the right shining through the evaporator coils:

Air Conditioner A-Frame Evaporator Coils: Interior Inspection Method

Air Conditioner A-Frame Evaporator Coils: Interior Inspection Method

In practice you should place the flashlight on the unobstructed side (i.e. left in my situation) of the coils, then wave it back and forth while watching the beam shine through to the far side of the cabinet. (It was easier to take the photo with the flashlight on the right side.) If the flashlight beam does not shine through the coils, that is strong indicator the interior of the coils are dirty. A small handheld mirror is useful to look back through coils towards the flashlight to see if the coils appear moldy or “hairy”.

Take care not to bump the coil fins with the flashlight or mirror because the fins are very delicate and bend easily.

Heavy Duty AC Evaporator Coil Cleaning

If the interior of the A-Frame coils requires a heavy duty cleaning, a hand-pump sprayer with Nu-Calgon Evap Pow’r-C AC evaporator coil cleaner is needed to shoot through the coils to clean and remove the interior dirt and crud. The pros use Nu-Calgon and you won’t find it at the big box home improvement stores. The spray wand can reach those tight spaces and the cleaning spray will loosen the dirt and mold off the inside of the coils. I had the evaporator coils at my former home in Florida cleaned this way by an HVAC technician because the air conditioner maintenance had been neglected by the prior homeowner.

Evaporator Coil Cleaner: Nu-Calgon Evap Pow'r-C 4168-08: 1 gallon bottle

Evaporator Coil Cleaner: Nu-Calgon Evap Pow’r-C 4168-08: 1 gallon bottle

Evap Pow’r-C is mixed 1 part evaporator coil cleaner to 3 parts water, so a 1 gallon bottle should be sufficient for many coil cleanings.

Nu-Calgon Evap Pow'r-C 4168-08: Evaporator Coil Cleaning Instructions

Nu-Calgon Evap Pow’r-C 4168-08: Evaporator Coil Cleaning Instructions

Evap Pow’r-C has an ammonia like odor, but not overwhelming.

Pump Sprayer AC Evaporator Coil Cleaning Steps:

  • Purchase a brand new hand pump sprayer in the 1 gallon to 2-1/2 gallon size.
    You don’t want to risk using an old pump sprayer that may have been used for weed killer, insecticide or other poisons!
    A 1 gallon pump sprayer is fine if your coils are not heavily soiled and only need a routine cleaning with 1/2 gallon of cleaning fluid & water mixture (remember to leave room in the sprayer for the air charge). A larger 2 or 2-1/2 gallon sprayer is convenient if your coils are very dirty and need a heavy cleaning with several applications of Evap Pow’r®-C.
  • Turn the air conditioning system Off.
  • Mix 1 part Nu-Calgon Evap Pow’r®-C evaporator coil cleaning solution with 3 parts water (hot water is better) according to the manufacturer’s instructions.
  • (Optional) For a heavy cleaning pre-soak:
    • Adjust the spray wand to a wide fine spray pattern.
    • Spray down the evaporator coils. Let the cleaning solution soak for 5 minutes.
  • Adjust the spray wand to a narrow 1/4 inch heavy spray pattern.
  • Methodically spray the down the coils; you should see the dirty cleaning solution running
    down to the condensate drain pan. Lots of dirt in the condensate drain pan means it’s working.
  • Check that the spray jet is not so forceful that it’s bending the coil fins.
    Most 1 and 2 gallon pump sprayers won’t generate enough force to be a concern, but larger sprayers may.
  • Wait a few minutes for the cleaning solution to run off the coils.
  • Check the condition of the coils with a flashlight as described above.
  • Turn On the air conditioner system.

The evaporator coil cabinet cover is removed to expose the A-frame coils. I’ve mixed 1/2 gallon of cleaning fluid which is 3 pints water + 1 pint Nu-Calgon Evap Pow’r-C in a pump sprayer. I don’t need a lot of cleaning fluid since my evaporator coils need only a routine maintenance cleaning.

Clean AC Evaporator Coils with Nu-Calgon Evap Pow'r-C

Clean AC Evaporator Coils with Nu-Calgon Evap Pow’r-C

Both sides of the A-frame AC evaporator coils are methodically sprayed with the coil cleaner. The spray wand is great for reaching way back in the cabinet. The cleaning fluid quickly wicked down the coils and into the condensate drain pan, which is good because it disinfects the drain pan and condensate drain line. In my experience there is almost no overshoot past the interior side of the coils even with a heavy focused spray. Verify there’s a healthy volume of cleaning fluid flowing in the drain pan and out the condensate drain line.

Evaporator Coil Cleaing with Nu-Calgon Evap Pow'r-C

Evaporator Coil Cleaing with Nu-Calgon Evap Pow’r-C

If you believe the coils need a second cleaning, wait an hour while the system is running for everything to dry in case some of the cleaning fluid dribbled onto the furnace heat exchangers, this way you won’t have the cleaning solution forming a puddle on the blower motor in the bottom of the unit.

Cleaning Inside the AC Evaporator Coils

The outside surfaces (or downwind) of the coils as shown in the above photo may look clean but the inside (or upwind) face of the coils can be dirty. See How to Clean Inside of AC Evaporator Coils for instructions on removing the coil cover plate and cleaning the coils with a pump sprayer and brush.

How to Keep the AC Evaporator Coils Clean

The #1 air conditioner maintenance item is to regularly change your air filter. A clogged air filter makes the air conditioner work extra hard, running up your electric bill. Check that the air ducts, plenums (rigid ductwork) and air filter housing are sealed to prevent unfiltered air bypassing the air filter. Unfiltered air which will turn your evaporator coils into dirt catchers. I seal the end of my air filter slot with a strip of metal foil HVAC tape to prevent unfiltered air being being drawn in.

Ultraviolet Light for Evaporator Coil Mold and Mildew Prevention

Consider installing an Ultraviolet Germicidal Light (UVGI) in the air handler to prevent and kill mold on the evaporator coils, drain pan and plenum:

Honeywell Ultraviolet Light Surface Treatment System UV100A1059 above AC Evaporator Coils

Honeywell Ultraviolet Light Surface Treatment System UV100A1059 above AC Evaporator Coils

Regular system checks by an HVAC professional in the Spring and Fall is recommended to ensure your air conditioning system is operating smoothly.

Hope this helps,

Bob Jackson

Copyright © 2019 HandymanHowTo.com   Reproduction strictly prohibited.


  1. KW Robinson July 31, 2012 at 10:37 am - Reply

    Very helpful in making me informed enough to do he job with confidence. Thank you!

  2. Bill August 14, 2012 at 10:41 pm - Reply

    You are a blessing Bob. Thank you for all the valuable information. I now have cold air again…and I am sure my utility bill will decrease.

  3. Don November 14, 2012 at 1:02 pm - Reply

    I searched the web for hours before finding your posting. You are an awesome teacher, and your pictures and your instructions were excellent. Thank you for providing such a great overview and directions on how to clean our air conditioner. I cannot thank you enough.

  4. James December 3, 2012 at 3:14 pm - Reply

    Thank You!

  5. Lisa January 10, 2013 at 4:15 pm - Reply

    Thank you so much for these how-to instructions. I feel like I can now clean my evaporator coils with confidence. I live in Texas and have a similarly set up system to the one you have. The pictures helped a great deal and were very well explained. I am going to share your website with my friends!

  6. Tim April 13, 2013 at 7:44 am - Reply

    Thanks for the information. I’m doing my pre-planning before I tackle this today. I’m concerned about being able to get clearance inside the cabinet where the coils are, enough to spray the aerosol can of cleaner.

    I’ve replaced other items on my furnace previously like the draft motor, and iginitor but this is the first time I’ve been inside the Coil Cabinet also a Heil, similar to your unit.

    Thanks again for the illustrations. If I can get some decent photos maybe I will try to send you some.

  7. Tim April 13, 2013 at 3:18 pm - Reply

    Follow-up … finished the chore after starting on it about 10:30 and taking 1 1/2 hr trip to Lowes to get a pair of metal snips to cut the housing in order to remove it from the input and output lines. The lines were not as dirty as I thought although 1 side seemed to be worse than the other. The one dirty side had more of a lime like scale which surprised me. The fin comb was great although cleaning the fins was very tedious. With it I was able to straighten some of the fins. I don’t think the unit had ever been accessed before. I will probably try the cleaner again in about 30 days. The one can of aerosol probably wasn’t enough.

    Thanks for the walk through. It gave me a lot of confidence to get it done.

    • BobJackson April 13, 2013 at 3:57 pm - Reply

      Odd that tin snips were required to cut the cabinet panel away from the refrigerant lines. Please send photos to bob (at) handymanhowto.com [replace the (at) with the @ symbol]. I’m happy you were successful. Now’s the time to clean the evaporator coils before warm weather sets in. Thanks for writing.

  8. Scott J May 16, 2013 at 10:13 am - Reply

    Thank you so much for this Bob, easy to follow and step by step. Saved me an expensive service call!!!!

  9. Andy June 19, 2013 at 9:43 am - Reply

    Hi Bob,
    I am very thankful I ran across your very detailed post.

    My unit looks exactly like yours pictured: A-frame evap on top, gas furnace in the middle, and blower on the bottom.

    I need your help! I have a 2006 unit and have a 5-7 second drip of water coming from underneath the furnace (looks like through a footer slot of the furnace) that is dripping down to the front side housing of the blower, onto the bottom of the unit, and pooling into my secondary drip pan at the very bottom of the entire unit.

    The primary 3/4″ PVC drain line leaving right from the A-frame evaporator was plugged up with rust sludge. But thanks to your posts, I have cleaned it out and verified that water is flowing down and out normally from the attic all the way outside.

    I even opened up the front sheet metal panel and viewed that the drip pan around the A-frame evap was draining water through the drip pan drain hole to the primary drain line.

    I completely emptied about 2 gallons of water from the secondary bottom drip pan to almost dry. Thinking maybe the drip is just water working itself out from the time the A-frame evap drip pan overflowed.

    I came back the next day and unfortunately the secondary bottom drip pan was about half full again from 1 day of the drip under the furnace continuing.

    I cannot access the furnace to see where the drip is coming from.

    But my guess it’s getting new water from the A-frame evap still.

    Do you have any suggestions? The A-frame evap drip pan is metal but is still shiny and no signs of rusting. Looks like it’s made of aluminum?

    Do you thinking I have a crack or hole in the A-frame drip pan? If so, how do I find it and how do I seal it up?

    This might be an odd question. But is the A-frame drip pan one solid square pan. Or is there a cut out/hole underneath the A-frame evap coils? Like a square punch out?
    I’m just wondering if water is dripping from the A-frame straight down the square punch out of the drip pan and then down to the furnace to the blower, causing the drip that I am seeing???

    Any advice you can offer would be very appreciative!


    • BobJackson June 19, 2013 at 6:17 pm - Reply

      > But is the A-frame drip pan one solid square pan. Or is there a cut out/hole
      > underneath the A-frame evap coils? Like a square punch out?
      The evaporator coil condensate drain pan (also known as a “drip pan”) is shaped like a race track with a large opening in the center through which the blower motor moves the air across the coils. An image of a A-frame condensation pan is here. Your pan would be look similar, whether it’s plastic or metal.

      > The A-frame evap drip pan is metal but is still shiny and no signs of rusting.
      > Looks like it’s made of aluminum?
      The water leak dripping on the furnace and blower motor housing might be caused by a rust hole or crack in the metal A-coil drip pan. It should be easy to confirm a drip pan leak by slowing pouring a pint of water in the back of the drip pan (drip pans are sloped back to front for drainage). Turn Off the AC and use a funnel attached to a small vinyl tube. Add some red or blue food coloring as a tracer. Test one side of the drip pan at a time. Wait 30 mins. Do you see colored water in the safety overflow pan below the unit? If so, your drip pan has a hole and you’ll need to call a professional to replace the drip pan because it almost always require removing the evaporator coils. Might as well replace rusty coils because the labor cost will be about the same since the refrigerant lines have to be cut to remove the coils.

      If the drip pan test does not indicate a leak, then the interior of your A-frame evaporator coils are “hairy” from mold and dirt buildup. The hairy or bumpy mold forms miniature stalactites on which condensate water collects and drips onto the furnace and blower motor instead of wicking down A-frame coils into the drip pan. The Florida Solar Energy Center has a nice photo of mold on the inside/underside of A-frame evaporator coils here. The updraft blower motor is in the forefront of the photo. The drip pan has obviously been removed in the photo so as to see the inside the A-coils.

      Have you tried the high intensity flashlight and hand mirror technique as illustrated in the project to get an idea if the inside of your A-frame coils are dirty? Try cleaning the coils with the commercial coil cleaner and pump spray wand. Two or three cleanings may be necessary. Dirty coils would be your least cost problem and easiest to remedy.

      Lastly, change the air filter regularly and make sure the filter is sealed such that air isn’t getting around the filter.

  10. EricM June 21, 2013 at 10:56 am - Reply

    Bob these are excellent instructions. The issue I have is I do not have an access panel. Should I cut one or just pull off the whole side. It appears to be glued to the other panels so I am afraid as I start to remove it, I will be in for a bigger project than I was hoping for.

    • BobJackson June 21, 2013 at 8:21 pm - Reply

      That is odd. The air handler installation manual and/or parts diagram can often be found online. Recommend writing down the make, model and serial # of your unit and searching online for the information. There might be a standard way to access evaporator coils. I wouldn’t pull apart the glued sheet metal seam because if it bends or warps, getting it back on will be very difficult.

      If there isn’t a way to open the sheet metal coil case (cabinet), install a Lau or Kees access door in the rigid plenum (air duct) above the evaporator coil case. The rigid plenum is easy to cut with a utility knife and there’s no danger of puncturing the evaporator coils. Install two duct access doors, one on each side of plenum above the evaporator coils to inspect and clean both sides of the coils.

  11. Richard P June 22, 2013 at 10:10 am - Reply

    Bless you Bob and guys like you for the help and hints. I had a basket filter and my newer installation only has a regular filter blowing outward. My cold air returns are sucking and feeding cat hair and small clay right up inside the A coil. I wonder how many extra nickels I gave to Com Ed over time. I was iced over like a 50’s freezer box and really don’t remember the last time the air flow was good. Shame on me. But, I have the A jacked up on blocks and am peeling the cat hair wallpaper from inside by way of the bottom. Not nice how the pipes run thru the wall sheet and there is no easy disconnect to clean this. Your encouragement saved me some big dough(which I do not have) and should have a decently cool house later today. Thanks again Rich in North Illinois.

  12. john June 27, 2013 at 10:59 pm - Reply

    have cleaned my evaporator but water leaks onto the floor underneath it when the fan stops running. wonder what I can do to remedy this.

    • BobJackson June 28, 2013 at 4:23 am - Reply

      See my reply dated 2013/06/19 at 6:17 pm to Andy for the same problem.

  13. Elin July 1, 2013 at 10:29 am - Reply

    I had to recently replace the evaporator coil in my 5yr AC, cost me almost $1500! a cost I was not expecting… why did the Plumber stated that it was clogged and had to replace it -couldn’t it have been cleaned? I was never told by the builder that this was something that required maintenance. Any advise?

    • BobJackson July 1, 2013 at 6:02 pm - Reply

      You’d need to ask the HVAC technician why the coils required replacing versus cleaning. 5 years is “young” – did you check the manufacturer warranty to see if it was still covered?

      It’s really not the builder’s job to explain all the responsibilities of home ownership. The builder should have provided a homeowner’s package with the user manuals and warranties for the appliances, including the air conditioning and heating system, where you’d learn about care and maintenance requirements. It’s best to assume everything needs maintenance from time-to-time.

      For HVAC systems:
      * Have a professional check the unit twice a year before the cooling and heating seasons.
      * Change the air filter regularly, once a month during heavy use.

  14. Robert H July 9, 2013 at 10:39 pm - Reply

    These posts have been immensely helpful. I was staring at the dirty coil earlier, not knowing what to do. Now I have a plan! Thank you!

  15. Matthew July 27, 2013 at 9:34 pm - Reply

    I appreciate all these instruction posts. My wife and I are first time home buyers and we’ve been in the house for 4+ yrs and to my knowledge have never had the unit serviced or checked. My capacitor went out at the start of this summer(blower motor) I was blessed on being able to diagnose and fix on my own.
    I checked my manual and it has an illustration showing an access door panel on the a-frame to acess the underside of the a frame , however mine doesn’t have this showing up on my a-frame sheet metal. Could I carefully cut a small door that doesn’t come near the coils but allows me to access the underside??

    • BobJackson July 28, 2013 at 12:52 pm - Reply

      Do you have an upright air handler (like mine) or a horizontal unit? What is the make and model # of your air handler and/or evaporator coils? The service manual is often available online and I’d like to review the manual.

      You can e-mail photos to bob (at) handymanhowto.com so I can see what you’re seeing.

      If an access panel is not available in the sheet metal coil case, it’s safer and simpler to cut an access panel in the supply plenum above the A coils. The section below the coils is normally the furnace and you want to stay away from that due to the presence of the control board, electric or natural gas heating elements and the risk of breaching the gas combustion chamber causing a carbon monoxide leak. Again, it depends on the configuration of your air handler.


  16. John July 29, 2013 at 7:25 pm - Reply

    Thanks Bob. Great job from a good teacher. I am a builder and have copied the links to your 3 articles, placed them in my “homeowner Help” folder and sent to some of our clients.

  17. Floyd October 3, 2013 at 8:11 am - Reply

    Love your articles. My problem is this. It did not seem that the air was blowing very well for my AC. I have had numerous companies over to work on the AC. The latest is that there was a technician that came over and put in some (Frepn?). He said that the coils were clogged with dust and that it would be 350 dollars to clean them. He did not take off the panel to see the coils. I took off the panel (it took me a while as there was a sealant painted over all of the seams) and the coils looked clean. I know what dirt looks like. After I looked at the coils I got two cans of the cleaner and sprayed down the coils a little at a time. i got a spray bottle and rinsed the coils. An hour or so later I sealed everything back up and started running the AC. It dropped the temp down from 79.5 to 76.5 in what I thought was good time. Ran the ac to get it down to 72. The smell from the chemicals was strong in the house last night. When I went to bed it was at 75. When I got up it was at 73 and the A coils were frozen over. I ripped all of the tape off of the seams and opened the panel. Did what I could to defrost the system. What caused the system to freeze over as there wasn’t any air blowing through once it froze over? I also put in a not as constrictive type of air filter in it also. Did I not wait long enough for the system to dry out prior to sealing it up? Should I have ran some heat through the system after cleaning the coils? How long should I have waited to let it dry if that is the case? Should I get another tech out to the house again. The last one was from the home warranty company and I am not trusting those type of companies as much. Would it have frozen over if the coils weren’t as dry as they should have been? Thanks for your help.

    • BobJackson October 3, 2013 at 7:52 pm - Reply

      > He said that the coils were clogged with dust and that it would be 350 dollars
      > to clean them. He did not take off the panel to see the coils.
      That strikes me as expensive and not doing due diligence by inspecting the coils. That doesn’t rule out the coils may in fact be dirty.

      > I took off the panel (it took me a while as there was a sealant painted over
      > all of the seams) and the coils looked clean
      The stiff rubbery sealant is mastic. Excellent for sealing air ducts and plenums. I prefer aluminum foil HVAC tape for sealing air handler access panels that need to be removed for maintenance.

      > I got a spray bottle and rinsed the coils. The smell from the chemicals was
      > strong in the house last night.
      That shouldn’t be so. Is the condensate drain line clogged?

      > When I got up it was at 73 and the A coils were frozen over.
      Low refrigerant charge can cause the coils to freeze, since the HVAC tech checked and topped off the refrigerant that can be ruled out.

      > What caused the system to freeze over as there wasn’t any air blowing through once it froze over?
      The coils are freezing because there’s insufficient air flow through the coils. The coils are a heat exchanger and low airflow won’t keep the coils above 32 degrees. When that happens the coils start icing which further blocks the air flow resulting in a vicious cycle (positive feedback loop). You’ve already changed the air filter, so we know that’s not blocking the air flow.

      Have you tried shining a flashlight through the evaporator coils to check if the inside (upwind) is dirty? A small hand mirror to view the flashlight shining through the coils is a big help. The downwind side (top part of the A frame coils in the project) can be clean, but the upwind/interior side is where the dirt and mold will accumulate first.

      Other possible causes of frozen AC coils are:
      * Weak or dirty air handler blower motor. Look at the blower wheel for heavy dirt build-up that will interfere with the aerodynamics. Normal blower fins will have a light/thin dusting, but thick fuzzy buildup on the fins means the blower efficiency is significantly reduced. Brush and vacuum off the heavy buildup. Remember to turn-off the electricity at circuit breaker before disconnecting and pulling the blower motor. If the blower motor fins are really dirty, then it’s likely the interior of the A-frame coils are too because what gets past the blower wheel will get caught on the coils.

      * Return or supply air vents are (partially) closed, constricting the air flow.

      If the coils freeze up again, open the air handler and wait for it to defrost. The flashlight trick to see through the coils will confirm the ice is melted. Running the air handler fan (fan only setting on the thermostat – no heat or AC) will help dry the coils. You can try turning on the heat, but read your owner’s manual first because I’d be concerned about thermal shock and cracked solder joints if the coils quickly go from freezing to hot. Normal system operation doesn’t call for cooling one minute and heat the next.

      > Should I get another tech out to the house again. The last one was from the home warranty
      > company and I am not trusting those type of companies as much.
      I’ve spoken to repairmen who said home warranty companies tell them their job is “To get us out of this”; do as little as possible, inexpensive temporary fixes, don’t exceed the cost of the service call. Repairmen who do the right thing risk losing the home warranty busine$$. A co-worker recently had a very bad experience with a home warranty company. Half a dozen trips to fix his AC were fruitless; do a few checks and say there’s no real problem. He fired the home warranty company and called the same HVAC company back (because they’re a highly rated large company) for a totally different service experience. The HVAC tech spent all afternoon at his house (I was present and took photos) and finally got to the bottom of it, there were multiple issues never mentioned until then. I’m not claiming all home warranty companies do a poor job, but my experiences have negative.

      Let me know what you find. You can e-mail photos to bob (at) handymanhowto.com

  18. Floyd October 4, 2013 at 8:54 am - Reply

    I had another company come out and he showed me what is wrong as you have mentioned a couple in your reply. My A frame coil is clogged completely on the right side as there wasn’t any air coming through it. Left side had some air coming through it. This is after I had put through a couple of cans of cleaner on it and rinsed with water. The tech said that the thickness of the coil frame makes it very difficult to get the dirt out. The blower area is dirty. He stuck his hand in there and pulled out some dirt and showed me. He is coming today to remove the A coil and blower and give them a cleaning. Pretty expensive. The question I think is who can afford to clean this system like this even once a year? How do I keep the A frame coil clean and how to I keep the blower area clean? I do not wish to have the A coil removed again. My central air unit is like the one that you have in the pictures. I will say that the room in the A coil area is a little tight. I do not like the smell of the chemicals that come from those cans of cleaner. As for the blower there has to be a way to keep that area clean. I can add the needed maintenance to my schedule as I do the main maintenance on my house in the months of Oct and Apr. One more thing. With the bedroom doors being closed how do I increase the air flow in the house? The 3 bedroom doors or closed at night and two of them are closed during the day. Spending alot of money on this type of maintenance is not something I wish to do again. Thanks for your help.

    • BobJackson October 4, 2013 at 10:31 am - Reply

      I’m glad you found the problems!

      > How do I keep the A frame coil clean and how to I keep the blower area clean?
      The #1 thing for keeping the blower fan and evaporator coils clean is to ensure air does not bypass the air filter. I use Filtrete “red” Micro Allergen 1000 MPR rated filters on my unit and never had a problem.

      When the HVAC tech is on site for the cleaning, ask him to check the return air plenum, start collars, duct connections and air filter slot for gaps. Seal the air filter slot with the aluminum foil HVAC tape. A UV germicidal lamp can help prevent mold growth – but it won’t do anything for raw dirt. UV lamps can be installed both above and inside the A-coils, depending on the particular lamp.

      > With the bedroom doors being closed how do I increase the air flow in the house?
      Closed doors shouldn’t be an issue if there are return air vents in the rooms. Each room should have a supply (fresh air) vent and return vent. How are your rooms equipped?

  19. Floyd October 4, 2013 at 1:04 pm - Reply

    Thanks for your reply. I will look into the solutions that you gave me and I will let you know what happens. As for the air return vent there isn’t any in my house. The only vents are the ones that push the air out from the central unit and the main one that pulls the air into the blower through the filter. I have two vents in the kitchen area, two in the living room, one in a bathroom that are not closed off by having doors closed. The rest are located in a the bedrooms and one in the master bathroom. Also, I was told to not use a filter that has many folds in it as it restricts the air flow. I put in a filtrete one that has less folds in it.

    • BobJackson October 5, 2013 at 10:03 am - Reply

      Every room with a door should have provisions for return air flow. When a room only has a supply air vent, no return vent and the door is closed, it’s like trying to blow up a balloon resulting in limited air circulation.

      The ideal solution is to install return air vents and branch ducts connected to the trunk duct. This can be easy or difficult depending on the layout and construction of your home. Take care that return air vents must be the permanently open non-louvered type. Return air ducts are installed using the same method as supply ducts, but connected to the return trunk duct:
      * How to Add a Room Air Duct for Heating & Cooling
      * How to Add a Room Air Duct with Speedi-Boot
      * How to Install an Air Duct in a Suspended Drywall Ceiling

      If installing a new return air duct branch line is not feasible, easy retrofit methods for providing a return air pathway are:
      * Simple pass-through transfer grille installed in the wall over the door
      * Transfer grilled installed in the lower part of the door
      * Jump duct in the ceiling between the bedroom and the hallway

      The rule of thumb for sizing transfer grilles is 1 square inch of grille area per square foot of floor space. This corresponds to the AC sizing general guideline of 1 cubic foot per minute (cfm) of air flow per square foot of floor space. See my comment dated December 14, 2011 at 11:00 am in this project for duct sizing details.

      > Also, I was told to not use a filter that has many folds in it as it restricts the air flow.
      I believe if you solve the return air flow problems and balance the air flow, the blower motor won’t have to work so hard. You’ll be able use the pleated air filters that do a better job of catching fine dust thereby keeping your evaporator coils cleaner.

  20. Serge January 4, 2014 at 7:26 pm - Reply

    Dear Bob:

    I have an 10 year old Carrier 5 Ton. Here are the facts: Furnace is horizontal in tight attic space; the fan speed is set at high/high; the return air was located 20 feet off the ground (previous owner) which has apparently caused the heat exchanger to have a rough ten years; the return has been relocated to ground level with 8″ x 24″ galvanized trunk and two 90 degree elbows; the furnace trip switch shuts off the gas flame after two minutes once reset; SEARS Blue Team examined furnace and noted that the coils appear to be dirty because air flow is very high immediately behind the air coils but about one third that level coming off the other side of the air coils (hardly any air flow comes out of the air vents); if the gas pressure valve is set at 0.9 water column, the furnace flame does not shut off but temperature only reaches 60 degrees; if set the the gas pressure valve is set at 3.0 (water column), the furnace shuts off the gas via trip switch; disconnecting the 8″ x 24″ duct work and permitting direct air flow to the heat exchanger with gas pressure valve set at 3.0 still causes trip switch to flip; SEARS is recommending Removing and cleaning the coils and running the unit without the coils all together to confirm that it was the coil issue, and once confirmed, then put back the cleaned coils to confirm no shut off at 3.0 gas pressure. No warranty on any work done b/c ten years old

    Question: Should I bother or just install a new Furnace and which brand would you generally recommend these days?

    • BobJackson January 5, 2014 at 12:06 pm - Reply

      > examined furnace and noted that the coils appear to be dirty because air flow is
      > very high immediately behind the air coils but about one third that level coming
      > off the other side of the air coils
      Dirty evaporator coils will block the furnace air flow and cause the furnace safety shutoff mechanisms to trip.

      The evaporator coils may need to be pulled per the SEARS Blue Team recommendation, but is there no means to inspect the evaporator coils short of removing the unit? What is the model # of the Carrier evaporator coil in the attic air handler? The evaporator coil configuration is important, e.g. slab coil, horizontal A or N coil arrangement.

      Depending on the availability of a sheet metal access panel and the coil arrangement it can be very difficult to access the coils. However, it should be possible to access the fresh air supply plenum and get a look at the down stream side of the coils. It’s not difficult and way less expensive to either remove a trunk duct or cut an inspection hole in a rigid duct board trunk versus pulling the coils. This may provide sufficient access to get a spray wand and coil cleaner at the evaporator coils. Much depends on your air handler and plenum configuration and materials. You can e-mail photos to bob (at) handymanhowto.com.

      I recently replaced the trunk ducts on my air handler for some ideas.

      > Question: Should I bother or just install a new Furnace and which
      > brand would you generally recommend these days?
      You’ll probably get a different opinion from everyone you ask. I’d start with the Consumer Reports Central air conditioning buying guide and Central air conditioning reliability survey.

      Determine your central air conditioner requirements. I’d look for the following features if were shopping for a new unit:
      * Furnace – gas, electric, etc.
      * Variable speed air handler – these are really nice.
      * Aluminum evaporator coil – never rusts
      * WiFi enabled thermostat with remote Internet access (I like technology. This can be an after-market thermostat.)
      * SEER rating
      * Whole house humidifier – nice to have in the cold season.
      * Manufacturer’s warranty – read the fine print.
      * Will the Dealer/Install reuse the copper refrigerant tubing or install new copper? How does this affect the warranty?
      * Dealer/Installer reputation and length of time in business
      * Dealer warranty for labor and possible installation problems.
      * Who will handle warranty claims? The dealer/installer should be the “one throat to choke” and responsible for all warranty service.
      * I’d ask to the see the dealer’s portfolio of installed jobs to verify they do nice looking work
      * Dealer customer references.
      * Are the dealer and HVAC technicians factory-certified in that particular brand of AC system.
      * How many (brand name goes here) systems does the dealer install per year?
      * Are the installers employees of the dealer or subcontractors? Stay away from subcontractors.
      * Check the Better Business Bureau (BBB) rating for the dealer.
      * Make sure the dealer files for a building permit and get the local building inspector to sign-off before final payment.
      * Compare three quotes to check price and list of services/warranties for omissions.

      Ask the dealer/installer to inspect your ductwork for problems and get a quote to have that corrected. Bad ductwork will defeat a new central air system.

      That said, I would focus on large manufacturers like Carrier and Trane that have been around for a long time. I bought a variable speed Trane XL system for my former home in Florida and was very happy with it.

      • Serge January 6, 2014 at 6:41 am - Reply

        Dear Bob:

        Bless your heart for responding in such a thorough fashion…It is indeed a rare instance that someone with all this knowledge at his fingertips will take the time to help out his fellow citizens-I must say, very refreshing indeed.

        In the meantime, I will follow all of your recommendations. the Carrier Model No. is 58MXA (fyi, the unit is installed on its side (left side, if that matters) due to space considerations, which seemed odd to me when we bought the home…

        p.s. Happy New Year to the Jackson’s and may you have all the health and prosperity you wish.

        • BobJackson January 6, 2014 at 7:52 am - Reply

          Hi Serge,
          The Carrier Model # 58MXA is that for the gas furnace only. Your system would be similar to the attic installation diagram on page 14. There should be a model # label on the evaporator coils. The AC evaporator coils and outdoor compressor unit is purchased separately to match the specific cooling requirements of the house.

          Thank you for the compliments!

  21. Nicole July 4, 2014 at 5:06 pm - Reply

    I have an A frame just like yours in my manufactured home.. I have replaced everything but the coil unit and it’s about 11 years old I don’t know much history because we just bought this house. Our unit keeps freezing up we have had a tech come out and he says there is the correct amount of pressure in the lines everything is running right, all I can think is the coil needs to be replaced because it’s not getting enough airflow. Could that be so???

    • Bob Jackson July 5, 2014 at 11:58 am - Reply

      Hi Nicole,
      The main causes of AC evaporator coils can freezing are:
      * Low refrigerant charge because it (ironically) lowers the gas temperature
      * Weak blower motor that’s unable to move enough air to keep the coils from freezing
      * Dirty coils that blocks the air flow

      Because the AC tech has checked the refrigerant charge and blower motor, that leaves dirty coils as the probable cause. Have you checked the interior side of your A-frame coils? The outside may look fine but the interior (or upwind) faces can be dirty. It may be possible to remove the coil front cover plate for cleaning but a lot depends on how your particular coil is made. If you’d like specific advice, remove the coil case outer panel and send photos of your coils to bob[at]handymanhowto.com – replace the [at] with the @ symbol.


  22. ron bonavico December 11, 2014 at 8:24 am - Reply

    My a frame doesn’t have cover plates. Is this ok

    • Bob Jackson December 12, 2014 at 5:28 pm - Reply

      There are many different AC evaporator coil configurations. If the A-frame evaporator coil doesn’t have endplates there should be something to prevent the airflow from spilling around the coils.

  23. Janie June 29, 2015 at 5:52 pm - Reply

    How do I find out if my drain pipe is clogged up on my a/c?
    There is a white pipe coming out of the pan, and a T pipe sticking up out of that.
    can I somehow disconnect the pipe coming out of the frame? My a/c tech is out of town
    he said to pour some bleach in the T sticking up to clean out the pipe..
    thanks, Janie

    • Bob Jackson June 29, 2015 at 9:34 pm - Reply

      Your A/C tech’s advice is good. You can also try running a flexible wire bottle brush down the T-pipe in case the U-bend is clogged. Don’t force the brush past the overflow safety switch – it’s the device with two small wires. Wear safety glasses to avoid bleach splatters.

      Whether or not the PVC drain trap and pipe can be disconnected depends on if there are threaded union fittings that can be unscrewed or more likely the pipe is permanently glued together.

      The Mighty Pump™ A/C Condensate Drain Line Pump is simple to use and does a great job if your A/C guy isn’t available for a week or more and you can wait for shipping.

  24. Karen August 31, 2015 at 2:15 am - Reply

    Hi Bob,

    I have an Armstrong air handler model # 065498509 and I know the coils are dirty. The tech has told me the only way to clean them is to remove them and rinse with acid for $500. I have read about the coil cleaners, can’t I just use that? If so which cleaner?

    • Bob Jackson August 31, 2015 at 8:10 pm - Reply

      $500 for evaporator coil cleaning sounds about right because it requires a lot of materials and labor:
      * drain the refrigerant
      * disconnect and remove the coils
      * clean
      * reinstall
      * draw a vacuum
      * recharge the refrigerant
      * test the system, check pressures, etc.

      The coil refrigerant lines are brazed connections (requires a torch) which requires training, skill and special solders.

      The alternative is to clean the coils in place as illustrated in the project. I’ve had very good results with the Nu-Calgon Evap Pow’r-C coil cleaner used in the project. It’s safe for metals and won’t harm your coils.

  25. Cody September 4, 2015 at 10:39 pm - Reply

    Thanks for the article. I’ve learned a ton about HVAC since I purchased my home, and it seems like we’ve had non-stop issues since we bought the place in 2012. In short, 2 condenser fans with new caps, a new compressor cap, then a whole new condenser unit. We’ve also had the blower motor replaced as it kept tripping the breaker.

    The issue we’ve had this summer is the system just not being able to keep up with the heat. We live in Las Vegas, so we had several weeks with highs over 110 degrees this year, but almost no humidity. For a week or two in there, the AC would run and never shut off and the internal temp would rise up to 6 degrees over our hold temp. HVAC companies really don’t like getting into the attic when its 115 outside, but I had a couple come, and they checked the system charge as well as superheat and subcool and said that everything was normal. It’s strange to me that our system would struggle, as its a 5-ton R-22 unit on an 1840sqft house. From everything I’ve read, that’s pretty oversized, but maybe they do that here in Vegas?

    I checked the delta across the return and registers and was getting 12-15 degrees, several below the expected 18-22.

    Anyways, I decided to inspect the coil myself, had to scrape off this awful dark-gray goop from all the seams on my evaporator cover and pop a bunch of spot welds keeping it closed (the installers really didn’t want me in there). Looking at the coil, there was a little bit of dust on it, but nothing like most of the photos I’ve seen online where its completely covered. Neither side looks dirty. I tried the flashlight method you recommended, and I don’t see any light coming through the other side at all. Could the internal coil and fin configuration that you can’t see be in a way to prevent light from getting through? I took one of the highly-rated foaming coil cleaners from Home Depot that had a coil brush as well and used the whole thing, but it didn’t seem to do much… maybe there was nothing to get. The home is 8 years old, and the evaporator had never been opened (as evidenced by the goop), so I doubt it’s ever been cleaned in the past.

    I’m just a little skeptical that everything is fine due to the cooling problems we’ve had this year, but if the superheat reading looked good, then there shouldn’t be an airflow problem over the evap coil.

    Any ideas?

    • Bob Jackson September 5, 2015 at 8:11 pm - Reply

      A 5 ton AC should make an 1840 sq ft house ice cold, even in Vegas. What’s the make and model # of your evaporator coils? With this info. I can look up the coils specs to determine if it’s a slab, A-Frame or W style coil.

      Since the HVAC techs have confirmed the refrigerant charge is fine I’d take a closer look at the ductwork (open joints, kinks, leaks), placement and sizing of the ductwork with the supply & return vents/ducts in each room and attic insulation.

      A 5 ton AC should be blasting cold air from the room vents as it requires at least 2000 cfm of airflow. How strong is the airflow from the room vents? If the airflow is just medium or weak there’s a blockage or the ductwork is too small.

      I’m thinking the home builder installed a large 5 ton AC unit but didn’t size the ductwork for the required larger airflow. The AC is running all the time but blowing air through a straw so to speak.

      • Cody September 6, 2015 at 2:47 pm - Reply

        Thanks for the reply!

        The evaporator is an A-Frame. Its likely a Lennox, as the furnace and original condenser were both Lennox, however, it has no make on the label. There is a model number though: CP60A3F-210T-014 13W67. (also says its rated for both R-22 and R-410A, with a “Design Pressure” of 350 PSI). I’ve scoured the internet for information on this unit, and I haven’t been able to find a thing.

        I’m always surprised by how little I feel air coming out of the vents. Most of them I have to really reach up close to feel it coming out. At neighbor’s homes I can feel their fents 6-8ft away easily. The original blower motor for my furnace was a 1hp 4-speed, which I think is really big, especially because they had a 3/4hp version on the same exact furnace. It was replaced about 2 years ago with another 1hp motor, so they told me. Its always run really loud, which I’ve read could be to an oversized fan/motor combo trying too hard to push a too much air through too small a space. My return size is 2 20″ x 25″ vents which reduce down to what looks like about a 24″ flex duct going into the bottom of the furnace. I believe my return size to be adequate, but I agree, and think the ductwork/register combination is likely too small for the CFM I’m pushing.

        Not long ago, there was an awful rattle coming through the return vent when the motor reached maximum speed. I tried to locate it, and just didn’t want to pull out the squirrel cage at this point, as that’s where it seems like its coming from. I noticed that it didn’t rattle hardly at all when running on medium speed, so I thought maybe that if the blower was oversized and noisy, running it at a lower speed may reduce the CFM down closer to what the ductwork can handle, and eliminate my rattle.

        I did that earlier this week, parked the high speed tap, hooked medium to cool, and low to heat, and think the air may be blowing a touch colder, as the air should be moving a little slower over the coil. The house actually feels chilly sometimes now, but that could also be due to the fact that our highs are currently only about 100 degrees.

        The house is 2 floors, so increasing the size of my ductwork on the first floor would likely prove to be extremely difficult, as there’s no basement and the vents are in the ceiling. The second floor, however, is where it gets really hot, so maybe swapping out the ductwork and vents in the bedrooms on the south side of the house for a size bigger could keep it a little cooler.

        I had suspicions about a blockage, possibly in the plenum, so I took a look while I was inspecting the coil. Everything looks clear. It looks like one of the trunks has a damper door on it, but it doesn’t move at all. There’s no external handle, and its definitely not electronic. Its permanently in the open position.

        I worry about the fact that I feel my airflow is already low, so adding larger vents will lower it even more to the rest of the house. I also worry about freezing my coil if there isn’t enough air movement with a slower fan speed, or overheating my furnace if I have it running on low in the winter. I’ve wanted to buy the tools to test the static pressure across the blower motor and the airspeed, but haven’t brought myself to do it. Maybe if I decide to switch to an variable speed ECM in the future I’ll splurge so I can get the speed set correctly.

        I also worry about fast-cycling both the condenser and the blower. I want to try to avoid having to replace them in 5 years, because they seem oversized for my home.

        • Bob Jackson September 7, 2015 at 9:47 am - Reply

          Given the weak airflow I recommend focusing on the evaporator coils. If the A-frame coils are reasonably clean and not iced over then you should be able to see through them with a flashlight and mirror. Ice would form on both the inside and outside of the coils indicating a low refrigerant charge. Yet the ice would melt when the system is Off for a while and then you could see the flashlight beam through the coils. For dirty coils you’ll need to remove coil end-plate to inspect the interior.

          The only reference I could find to your Lennox evaporator coil model CP60* is another homeowner in Las Vegas with cooling problems in 2009. Maybe you bought the same home in 2012?! If so the AC system has a long history of troubles.


          You may want to have a look at the Thomas v. Lennox Industries Inc. Settlement website and the coil class action settlement details. The lawsuit is about coil corrosion that causes refrigerant leaks.

  26. Cody September 9, 2015 at 3:01 pm - Reply

    You know, it’s strange. There is no triangular coil cover on my evaporator coil like is shown in your pictures. My unit lays on its side rather than upright, and the A frame is oriented differently as well. Instead of the two sides angling to make an arrow in the direction of the airflow, it’s like it’s pointing back into the furnace. Everything I’ve read online said that this is normal, and just depends on the orientation of the system as a whole, and is also common in down flow units. To have a cover on the furnace side of the coil, it would have to be two triangles on the edges instead of one in the middle.

    I’ve kind of assumed that my coils aren’t really that dirty, despite not being able to see through it with a flashlight, simply because they don’t freeze up at all. Now, maybe that’s more of a result of there not being enough humidity in the air here to condense on the coils, and therefore not building up any ice.

    I’ll check out the lawsuit and the other link. Thanks again!

  27. Sean McCarthy March 7, 2016 at 11:26 pm - Reply

    Thanks for the wonderfully precise description and super-helpful graphics & photos! If you ever come to Minnesota, email me so I can buy you dinner!
    Thank you SO MUCH!

  28. mike September 25, 2016 at 9:18 pm - Reply

    Great article! I have an A-frame just like illustrated.

    My problem is that the air coming from the ducts is not very cold. Nothing is icing up, filter and coils clean, the copper U-tubes at the ends of the A-frame on the coil are very cold, and the smaller little copper lines connect to a larger tube (leaving the bottoms of the coil is very hot.A-Frame fins inside and outside are clean..

    Can it be a low charge even if the copper tubes are cold, but no freezing?

    • Bob Jackson September 26, 2016 at 7:46 am - Reply

      A low refrigerant charge reduces the efficiency and cooling capacity of the system. The coils can still feel cold or even ice over, however the system will struggle to cool the home.

  29. Maribel June 13, 2017 at 5:34 pm - Reply

    Great articles on how to maintain ACs Bob. I have a lot of cats and just purchased a home and a brand new Trane 4 ton AC for it so I want to keep the unit in tip top shape. One question for you – in my old apartment I used to buy for the AC expensive 3M Filtrete Filters to try to protect the unit as much as possible from cat hair. When I had the new Trane AC installed in my home, the installers told me to just use the regular type filters they were providing since those would allow more air to pass through than the more expensive filters. Recently I had the first maintenance checkup done and the guy who did that told me that the more expensive filters would be better. So what’s your opinion on this? Are the cheaper filters better because they allow more air to get through? I change the filter every 3 weeks so financially it would be better to use a cheaper filter but if those cheaper filters are going to allow more cat hair through, then I’m probably better off with the more expensive filters long term.

    • Bob Jackson June 13, 2017 at 6:27 pm - Reply

      High efficiency filters do impede the airflow more than standard filters. If you have dander, dust mite and pollen allergies then a high efficiency filter is best. Changing the filter regularly and sealing the filter slot to prevent drawing in unfiltered air are the most important items.

  30. Cliff June 29, 2017 at 4:55 pm - Reply

    Where did you purchase the Nu-Calgon? The local supply shops near me only sell to professionals and not the public. I see it on Amazon but it is more for shipping than the product itself.

    • Bob Jackson June 30, 2017 at 8:42 am - Reply

      It’s free shipping with an Amazon Prime membership.

      • Cliff June 30, 2017 at 11:26 am - Reply

        I don’t think that’s as “free” as they make it look. There is a 3rd party seller selling it for 7.63 plus $17 shipping, or you can get it for $25 with “Free” shipping with amazon prime. lol.
        This makes me believe getting it at a local B&M store would be about half the price as the Amazon prime deal, if I could find one.

        But, $25 is still way cheaper than paying someone else to do it.

  31. Lonnie July 28, 2017 at 7:11 pm - Reply

    Why do my A-frame coils not have a cover. I’m in a 97 doublewide trailer. The inside unit sits in own closet with an air filter in the cut out part in the door of the closet. Is there supposed to be a casing around the A-frame coils also?

    • Bob Jackson July 29, 2017 at 11:27 am - Reply

      What is the make and model # of your air handler? Are you certain it’s an A-coil? Packaged units often use a slab coil which is different than an A-coil.

  32. Ian Journeaux May 27, 2018 at 12:48 pm - Reply

    I would like to look at cleaning my ac evaporator coils. My system looks a lot like the one you pictured but it is wrapped in insulation and well taped/sealed. Is it worth while opening up to clean coils? Furnace is 17 years old. Doubt it has been opened up before.

    • Bob Jackson May 27, 2018 at 9:04 pm - Reply

      There are cased and uncased evaporator coils. Cased coils are installed at the factory in a sheet metal cabinet. My system has cased coils with insulation inside the sheet metal housing. Uncased coils are just that; the installer fabricates a rigid duct board box to house the coils; it’s similar to making the supply plenum. The duct board seams are taped then sealed with mastic.

      Let’s assume you have uncased coils. You’d cut a front panel out of the duct board with a sharp serrated knife, inspect and clean the coils, then tape the panel back with metal foil HVAC tape, followed by sealing with mastic.

      Before doing any of that, I’d have an HVAC technician do a system health check. A 17 year old system is likely low on freon (R-22) and may have other problems. The tech can measure the temperature drop across the coils and infer if the coils are dirty/obstructed, refrigerant charge is low, compressor is failing, etc.

  33. Michael July 17, 2018 at 5:03 pm - Reply

    Bob – quick question. I replaced my AC Condenser 3 years ago. I turned on the AC unit and there is sufficient air flow however the air is not cold. It seems as though the compressor turns on and works for a short period of time and then turns off. I can hear it shut off. My question is, could dirty and/or faulty evaporator coils shut down my compressor? HVAC guy is quick to tell me replace the entire unit because of a “bad compressor.” He never looked at the evaporator coils.

    • Bob Jackson July 18, 2018 at 8:19 am - Reply

      A refrigerant leak could cause the compressor to short cycle, but the leak could be anywhere. The compressor can shutdown for a number of causes: bad running capacitor, thermal (overheating) shutoff, low refrigerant charge, etc. Did the AC guy run a full system diagnostic? Check the:
      * capacitors
      * current draw with an ammeter
      * refrigerant charge by hooking up the gauges
      * temperature drop across the evaporator coils
      * condenser fan is running properly

      If the system leaking refrigerant, the technician can do a UV dye and bubble test to find the leak.

      A compressor should last much longer than 3 years. Call a different HVAC company for a second opinion.

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