How to Clean AC Evaporator Coils

How to clean AC evaporator coils with no-rinse spray foam cleaner for routine seasonal maintenance. If you’re not comfortable cleaning the AC evaporator coils yourself at least you’ll what’s needed when calling a Heating, Ventilation and Air Conditioning (HVAC) professional.

Table of Contents

  1. How to Clean AC Evaporator Coils (this project)
    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
    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 Air Handler Components

The following photo is the central air handler in my attic. It is known as an “upflow” type because air enters from the bottom and exits out the top.

Attic Air Handler Components

Attic Air Handler Components

The unit combines a natural gas furnace and an air conditioning evaporator coil. It has three major sections:

  1. Blower motor – bottom
  2. Gas furnace – center
  3. A/C evaporator coil – top

The entire air handler sits on a secondary drain pan with a cutoff float switch. The purpose of the secondary drain pan is catch water in case the condensate drain line becomes clogged or the main condensate pan rusts through. The secondary pan will catch the water and eventually activate the float switch to shut down the entire unit before it overflows and ruins the ceiling.

The blower motor forces air upward (recall my air handler is an “updraft” or “upflow” type) through the furnace and air conditioner evaporator coils. The Heat and Cool functions of the thermostat ensure that either the furnace or the air conditioner operate, but never both at the same time. The supply air plenum box sits on evaporator coil sheet metal cabinet. Two large flexible ducts are connected the plenum box. The large trunk flex ducts connect to rigid duct board distribution trunk ducts that lay on the attic joists. Several smaller flexible duct branch lines are taken off the rigid trunk duct to supply air to vents throughout the house.

HVAC Air Handler Evaporator Coil Cabinet, Plenum and Flexible Ducts

HVAC Air Handler Evaporator Coil Cabinet, Plenum and Flexible Ducts

Update: The compressor was failing on the 17 year old AC system. I had the entire central air conditioner and furnace replaced with a Bryant Evolution high efficiency system. The new Bryant system is blows so much colder and reduced my electric bill by 20%.

New 3 Ton Bryant Evolution Attic Air Handler

New 3 Ton Bryant Evolution Attic Air Handler

How to Clean AC Evaporator Coils

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.

The evaporator coil access panel must be removed to access the coils. This is a closeup of the evaporator coil access panel, which is fastened with nine 1/4 inch sheet metal screws and sealed along the bottom with metal foil HVAC tape.

Evaporator Coil Cleaning: Evaporator Coil Case and Access Panel

Evaporator Coil Cleaning: Evaporator Coil Case and Access Panel

Remove the access panel screws with a socket wrench and peel away the metal foil tape along the panel edges (if any).

Remove the Evaporator Coil Access Panel

Remove the Evaporator Coil Access Panel

The access panel is removed exposing evaporator coils:

AC Evaporator Coil Cleaning: Access Panel

AC Evaporator Coil Cleaning: Access Panel

My system has an A-Frame style coil with a removable end plate. Your unit may have an N or slab coil which can be more challenging to access for cleaning. The evaporator coils are basically a heat exchanger, cooling the air inside the house and transferring the heat to the outside condenser unit.

A-Frame Evaporator Coil

This article is continued in How to Clean AC Evaporator Coils – Part 2.

Take care,
Bob Jackson

Copyright © 2019   Reproduction strictly prohibited.


  1. Faith July 14, 2009 at 8:30 pm - Reply

    Thanks for providing this information to your readers. This would really give them a helping hand to learn more and would give them idea on how to clean their own air conditioners at home.

  2. Ray Winter August 21, 2009 at 11:03 pm - Reply


    Thanks for this information. Gave me the confidence to inspect mine and clean them. They were absolutely filthy! I never imagined they would be after just 8 years.


    Ray Winter

  3. gary January 4, 2010 at 6:42 pm - Reply

    if i use the frost king cleaner in the winter, will i need to rinse?

    • Bob Jackson January 4, 2010 at 7:54 pm - Reply

      I think your concerned about the A/C being shut off in the winter and therefore no water condensation to further rinse the coils as there would be in the summer when the system is running. The instructions say it’s a “no rinse” product and I didn’t see disclaimers about seasonal/winter use. The foam breaks down nicely and drains away. You might shut off the heat for an hour so the fluid can do its work.

      A second application at the start of summer wouldn’t hurt if in doubt.

      • Julie January 1, 2015 at 4:04 am - Reply

        Hi, Bob. This looks like a bunch of great advice for me. I’ll have to see if any of it works tomorrow… In the meantime… My heater unit “blows” air, but, for some reason, within the large box-like unit in my attic, that hot air is not coming out of it into the tubes that go to the individual registers in each room of my house. A tech pointed at a section of the unit and said, “… air is being blown, but ‘something’ in this area is not allowing the air to exit and go into the vents….” Gee! Bob! What could that “something” be??? Filter? Coils? Darn dead animal body in it??? This sudden cold snap in CA is freezing my ears off! What could this problem be? Heeeellllp!

        • Bob Jackson January 1, 2015 at 1:14 pm - Reply

          Hi Julie,
          The “large box-like unit” your attic is the air handler.

          What did the HVAC Tech do during the service call? A routine maintenance check would include changing the air filter, checking the blower motor and furnace operation. If he suspected the evaporator coils are clogged he should have offered (perhaps for a small additional fee) to open the evaporator coil case to inspect the coils.

          If the air flow is severely impeded it’s possible the furnace will automatically shutdown to prevent overheating.

          > air is being blown, but ‘something’ in this area is not allowing the air to exit and go into the vents
          It could be a dirty air filter and/or evaporator coils. Perhaps a piece of insulation has come loose inside the return or supply air plenums and is blocking the duct. It’s also possible a duct joint has failed allowing hot air to blow into the attic.

          Also see these projects for more information:
          * How to Clean Inside of AC Evaporator Coils because most of the dirt will be on the upstream (or interior) face of the coils.
          * How to Install Round Sheet Metal Duct which goes into the great detail about ductwork.

          I think you’ll quickly find the problem starting with the basics:
          * Air filter check.
          * Remove the evaporator coil access panel, check for blocked/dirty coils and loose insulation.

          Be sure to turn off the circuit breaker before working on the system.

          You can send photos to bob[at] for specific recommendations. Include the make and model of your air handler and evaporator coils.

          Good luck!

      • Linda Crowther January 4, 2017 at 3:30 pm - Reply


        I had an A/C company come over today because my drain line was plugged and water started leaking down from the unit on to the floor of the garage. Apparently the overflow valve did not work. Now I am told that the insulation up inside the unit is wet and it needs to be replaced. They want $1,500 to open up the unit and dry out and replace the insulation, which includes new overflow valves. Is there any other way to dry out the insulation that is less costly?



        • Bob Jackson January 5, 2017 at 7:42 pm - Reply

          Is there an access panel on your evaporator coil case? If so, remove the panel to inspect the coil case insulation to make sure it hasn’t come unglued and fallen away from the walls of the case. If the insulation is still attached but wet along the bottom you can do one of several things:
          A. – If the blower motor forces air through a furnace/heat exchanger located before the coils (like my system) just turn on the heat. The hot dry air blowing through the coil case to quickly dry out the insulation. Reinstall the access panel first, of course.
          B. – If air handler configuration A. above doesn’t apply, reinstall the access panel and run either furnace or A/C depending on the season. The insulation will dry out soon enough due to air circulation. If your thermostat has a separate “Fan” control set it to On so the blower motor runs continuously even when the system isn’t actively heating or cooling to speed the drying.

          The condensate pan drain plumbing, P-trap and/or safety overflow pan float switch must be fixed but this is at most a couple of hundred dollars labor & materials.

          See How to Install Round Sheet Metal Duct for additional photos of the air handler plenum and foil-faced evaporator coil case insulation.

        • Just Me January 13, 2018 at 12:01 pm - Reply

          If what you mentioned is the only thing they will do then you are getting ripped off. For $600 I can re-insulate my entire attic with blown insulation (done myself) of a 2200 sq ft 2 story house, including renting the blower. Shutting the unit off, opening it up and drying it will only take about 2 hours of your time. Use sponges, towels, a bucket and a hair dryer. Done. Insulation can replaced too, as long as there are removable panels. Sometimes, some of the panels are riveted or are 1 large piece that make taking it apart an ordeal. A great way do do it is to loosely wrap the entire unit in plastic with enough room for a dehumidifier. Your basically making a little tiny room with plastic walls. Tape the edges of the plastic to the air handler ,essentially closing it off to the outside air. Turn the dehumidifier on and let it go to work for 8 hours. I don’t recommend using the fan only. The unit is a closed system and will just recirculate the humid air. That very humid air has a high risk of mold growth in the ducts. If you do want to run the fan only, I suggest several small dehumidifiers be placed in a few rooms do help quickly dry out the air and the insulation in the unit. The overflow valves an be purchased yourself & replaced. The old one may be able to be cleaned. If you cannot do all of these suggestions then maybe do a few to save yourself several hundred dollars.

  4. Cindy June 8, 2010 at 4:38 pm - Reply

    Many thanks….as a single mom, I winced at having a tech come out and charge me for something that I could do if I knew how.

    • Bob Jackson June 9, 2010 at 7:09 am - Reply

      I’m pleased the article helped you. Often times the work is not difficult, the problem is finding the specialized knowledge to do the work.

  5. George June 18, 2010 at 10:55 pm - Reply

    Ok I am having issues.. I have had numerous problems with my 3 ton intertherm heatpump. Just about 4 years ago I had a defrost board replaced. Then a fan motor outside the unit.. 3 years ago I had a compassador replaced. Last year I had a tech check out my attic unit and he told me my coils and everything were amazinely clean.. Two month later I need a fan wheel changed, looks like a rat wheel. Ok 2010.. I noticed a dimming of my lights and a few days later a tech came out and told me my compressor was gone, and also whomever hooked up my compassador had the wires backwards and thus my compressor went bad..

    Ok the tech replaces the compressor, then the tech tells me I have another huge problem, that my reversal valve is bad and also maybe my defrost board.. So I was a freaking week in 90′ weather and a different tech comes out and is walking round and round and is on his phone, comes to me 10 minutes later and tells me my unit is fixed and all it needs was a screw for the defrost board and a little piece of plastic behind it.. He left but my air wasn’t blowing as hard or cold, a little cool, it took almost 3 hrs to cool home down from 110′ to only 78 while on 68′ thermostat.. Now here is another problem, I come home and unit is on 71′ thermo settings it’s says 79′ on reading and it’s not so cool. So, I call the tech and he tells me I need a good coil cleaning, never looked up stairs in the attic and just because my outside unit is a little dirty but I keep it clean.. I then go outside to rinse down unit and I see my compressor copper pipe to another unit that looks like a huge soda can dripping, then that copper pipe to the pipe outside the unit into the wall with insulation wrap and all pipes are frozen.. I tell my son to turn off the unit and the frozen ice disapears instantly. I tell him to turn it on again and the rightside of all copper pipes because to freeze and the whole pipe turns frosty..

    what do you think is the issue, the idiot tech tells me I am mistaking and if I get all of my coils clean I will have better cold air.. It’s ludircrous.. Maybe I do need a cleaning, but one tech tells me my defrost board needs replaced because his reading weren’t correct and the connection wasn’t right or the reserval valve is shot..

    Why would my outside pipes frost up and no real cold air inside my unit..

    Lastly, I have a contract for the great AHS. American Home Shield and the fly by night idiots are amazing.. One company tells me the other screwed something up and this is why you have so many problems and then one tech from the recent company tells me after he replaces my new compressor I have other issues and a new tech from the same company screws the defrost board together and does his reading and leaves, what is a customer to do.. thanks for any help..

    • Bob Jackson June 19, 2010 at 9:00 am - Reply

      There’s so many issues going on that you should have an full installation audit of your Intertherm heat pump. Contact an authorized Intertherm distributor to explain your problems and order an audit.

      If you’ve been working with the local Intertherm dealers and believe that’s part of the problem, contact the manufacturer – NORDYNE – at:

      Customer Service
      8000 Phoenix Parkway
      O’Fallon, MO 63368
      Phone: (636) 561-7300

      > Lastly, I have a contract for the great AHS. American Home Shield and the fly by
      > night idiots are amazing..

      AHS should be sending only Intertherm authorized HVAC technicians to service your system. AHS has had their share of complaints and lawsuits.

      > Why would my outside pipes frost up and no real cold air inside my unit.

      The outside pipes are frosting because refrigerant gas is (too cold) inside the pipe on its way to the compressor. The pipes will be cool, but something sounds wrong if the pipes are freezing, like the evaporator coil inside the house isn’t working right. The evaporator coil is a heat exchanger that flashes the warm liquid refrigerant to a cold gas through an expansion valve. The cold gas circulates through the evaporator coils as the fan blows warm inside air over the coils. The indoor air gets cold and the refrigerant gas warms up. If the gas is below 32F as it returns to the outside compressor, then the cooling process isn’t working as it should and you’re too warm. The problem could be a number of things: bad expansion valve, wrong gas pressures, compressor problem, etc. The exposed pipes should be insulated, too.

      Post back and let me know how your situation is resolved.

  6. Dan July 10, 2010 at 10:37 am - Reply

    Thanks for a well written DIY article and good pictures to help illustrate what is involved.

  7. Alan August 27, 2010 at 12:10 pm - Reply

    Thanks for the great article. After I gained access to clean my coil, I saw that my A-Frame coil does not have a top, so to speak. I’m referring to the flat piece of metal which sits on top of both coils, at least in the pictures I’ve seen. Witout this piece, there is about a 2 inch gap between the coils. This would seem to be an issue to me, as the air-flow can move thru this gap without being filtered thru the coils. Is this an issue I should adress? Thanks.

    • Bob Jackson August 28, 2010 at 8:04 am - Reply

      You are correct – a missing A-frame cap will allow air to bypass the coils lowering efficiency. Contact an HVAC company and maybe they can fit a new cap. Makes me wonder what happened to the original cap? Did it come loose and get blown into the plenum or ductwork and is stuck up there blocking the air flow? You should have a look with a flashlight and small mirror.

      • Kathy Kocharian July 18, 2017 at 10:20 pm - Reply

        Hi Bob! Please help! My blower motor went out and they replaced it, but then we heard a squealing noise. He said the wheel got bent from blower motor going out. Is that true or did the wheel get bent from his work? Tech arrived today with new wheel $191.00 and work for 1 1/2 hr and said wrong size so he had to order another one from manufacturer. Temp was 84° in house when he turned on AC and left. Later, I felt the vent air and it was like a fan not cool air. Finally, 1 hr later, the AC IS BLOWING REAL COOL AIR. IS THAT NORMAL?? Thank you for your advice. KATHY K.

        • Bob Jackson July 19, 2017 at 12:25 pm - Reply

          If the fan wheel was stuck to motor shaft after loosing the set screw it might have been bent if handled too roughly. I think it more likely the center hub of the fan wheel that rides on the motor shaft worked loose allowing the wheel to wobble especially if the motor bearings were failing. The Tech should’ve noticed a loose/out of balance wheel when the motor was replaced or immediately after restarting the AC. The squeal was caused by the fan wheel rubbing against the housing.

          > Temp was 84° in house when he turned on AC and left. Later, I felt
          > the vent air and it was like a fan not cool air. Finally, 1 hr later,
          The average temperature drop across the evaporator coils is about 20 degrees F. It was 84 degrees and probably a bit humid when the AC was restarted. The initial cooling load will be removing the humidity which has a high latent heat factor; the air is drying but there is very little change in temperature.

          As the air dries and less cooling load is consumed by latent heat (water condensation with minimal change in temperature) the air temperature across the coils drops more quickly. Instead of dropping from 84F to say 78F, it’s the full 20 degrees and progressively getting cooler & drier. So 1 hour for the system to fully acclimate is not unusual.

  8. Alan August 28, 2010 at 7:55 pm - Reply

    Thanks for the advice Bob, I’ll definitely check into it further.

  9. Brigitte March 21, 2011 at 2:21 pm - Reply

    Hi Bob,
    How do I remove the evaporation coil for cleaning? If this is too difficult or risky. Is there a good way to clean it efficiently without removing it?

    • Bob Jackson March 21, 2011 at 7:27 pm - Reply

      The evaporator coils cannot be removed for cleaning because the refrigerant lines are permanently connected and would have to be cut.

  10. hoppinjohns April 23, 2011 at 4:41 pm - Reply

    Your post got me started to clean my HVAC coil. Your pictures are great and particularly helpful.

    Mine is a horizontal installation because of its greater size. It’s more difficult to work with but exactly the same steps as yours.

    I went one step further to take the side metal sheet off so that I can wash, spray, and vacuum from the inside side of the evaporator coils under the coil dome. My coil inside is filled with insulation feathers, the type of insulation the builder pumped into attic. A few years ago, the intake air return was loose and fell off half way. The AC sucked in a bunch of insulation. They were trapped on the coil but on the inside side. They probably blocked a significant amount of air flow, not to mention the bad air they produced. It took me a long time to vacuum them off. I made a special vacuum head to use on the delicate coil.

    Thanks for your posting.

    • Bob Jackson April 23, 2011 at 6:06 pm - Reply

      Wow! I can just see all that blown attic insulation plastered on the face (upwind side) of the evaporator coils. You were fortunate to discover the problem and clean it off. I’ll bet your electric bill this August is 30% to 40% less than last year!

      Thanks for sharing your experiences.

  11. Theresa Bell May 17, 2011 at 1:23 pm - Reply

    My daughter is having a home inspection problems. The owners or agents are not completing the work to the satisfaction of the inspection, who has made 2 trips. The problem, according to her home inspector is the coils are shot. I recommended that she take the advice of the person she is paying, her home inspector, ask for her earnest money back and start looking for another home.

  12. chris lenahan June 12, 2011 at 11:15 pm - Reply

    I have a mobile home 14×66. I i have an intertherm 13-seer. Where are is the a-coil locacated. is this the same as the evaperator coil? is it located in the outside unit or somewhere underneath my home or inside the house. I perplexed. i cleaned the outside coils in and out changed the thermostat and still not working properly. please help. thank you

    • Bob Jackson June 13, 2011 at 6:42 am - Reply

      > Where are is the a-coil locacated. is this the same as the evaperator coil?
      The evaporator coil is inside the air handler and may be a flat style coil (like a car radiator) or an A-frame style.

      > is it located in the outside unit or somewhere underneath my home or inside the house.
      The air handler could be underneath the mobile home or inside a closet. It would help if you provided the model # of your Intertherm A/C unit.

      > i cleaned the outside coils in and out changed the thermostat and still not working properly.
      Have you changed the A/C filter? Look around the house for a main air intake duct, it may be next to the air handler. A clogged A/C filter will restrict the air flow, interfere with cooling and run up your electric bill because the unit will be running longer than necessary.

      You may want to call an air conditioner service company to inspect your unit and perform a seasonal tuneup – check the refrigerant charge, inspect the coils and electronics, change the air filter, etc. They can show you where the air handler and air filter are located. Cost is typically in the $70 to $80 range.

  13. joel July 6, 2011 at 10:32 pm - Reply

    my unit looks like the above pict. but the header section isn’t insulated above the evaporator. the ducts are insulated upto the distribution header box but not the header itself; shouldn’t the distribution header box be insulated also/ what type insulation? Attic very hot here in South Texas..Takes awhile for just main cold water line to cool down from one end of house to other end!!

    • Bob Jackson July 7, 2011 at 4:53 pm - Reply

      The sheet metal header box above the evaporator coils should be insulated. Do you evidence the interior insulation duct board is missing? You could cut and fit sections of fiberglass duct board inside the box.

      1. Turn off the system and lay a towel or piece of cardboard over the coils to protect them from overspray.
      2. Measure the sides of the header box and cut sections of duct board to fit. “Dry” fit the boards to get everything perfect. The foil side will be showing.
      3. Spray the fiberglass side of the ductboard with a generous coat of 3M™ Super 77™ Multipurpose Adhesive.
      4. Spray the interior sides of the header box with the 3M Super 77 spray.
      5. Wait several minutes for the 3M Super 77 adhesive to bubble up and become tacky. Instructions are on the can. This will create a permanent bond.
      6. Press each section of fiberglass duct board to the side of the header box, foil side showing. Take care to align it perfectly as you won’t get a second chance.
      7. If you happen to cover up a duct hole, you can cut out the opening with utility knife after setting the duct board. Start in the center of the duct hole and work your way to the perimeter of the circle.
      8. Remove the towel or cardboard protecting the coils before closing up the header.

      Foil faced fiberglass duct board can be purchased from a HVAC or Building Supply company.

  14. Morgan July 11, 2011 at 12:34 pm - Reply

    to clean the coils, all i do is spray them with a cleaner or wipe down as well after spraying?

    • Bob Jackson July 11, 2011 at 4:46 pm - Reply

      Spray the coils with the foaming cleaner. Do not wipe or touch the coils because the fins are delicate and will bend blocking the air flow.

      • Derek January 4, 2014 at 12:17 pm - Reply

        Is Web coil cleaner a good product.

        • BobJackson January 4, 2014 at 1:41 pm - Reply

          Web coil cleaner is intended for the outdoor compressor coils. Because the aerosol can contains propane and butane the Material Safety Data Sheet (MSDS) states:


          My recommendation is to only use the product on the outdoor compressor coils. A different cleaner is needed for the indoor air handler evaporator coils.

          WEB Coil Cleaner does have favorable user reviews on

          • Derek January 4, 2014 at 6:16 pm - Reply

            What cleaner should I use for my indoor evaporator coils?

            • BobJackson January 5, 2014 at 10:53 am - Reply

              I understand the confusion now. The Frost King brand no-rinse cleaner has been discontinued. The new brand made by the same company is the Thermwell Products AC-Safe Air Conditioner Coil Foaming Cleaner. See the update with product links in How to Clean AC Evaporator Coils – Part 2.

  15. Steven Swann July 22, 2011 at 4:44 pm - Reply


    You start by asking if the filter in the AC unit (shown in your pictures) should be changed.

    You go on to explain how to change the coil, but don’t answer the question about the filter on the air handler.

    Should it be changed? Monthly?



    • Bob Jackson July 22, 2011 at 6:32 pm - Reply

      Change the filter monthly as a rule.

      But… I have Honeywell touch screen thermostats in my home. The Honeywell keeps track of the total run time since the AC filter was last changed and displays a “Change Filter” message after 10 running days. This is about every 2 weeks in July/August and January/February in the Atlanta area where I live. Much longer when the weather is mild and I have the windows open in the Spring and Fall.

  16. Felice July 25, 2011 at 10:32 am - Reply

    Hello, the air in that my chiller unit blows out is moist and not
    very cold. At around 9pm the temp. inside is about 75 degrees, and
    the thermostat i put at 70, hoping to cool down the temp. to no avail.

    As i understand it, my chiller unit in my condo unit takes cold liquid from the main
    boiler room which is about 40 yards away in another building and somehow
    is brought to my unit’s hvac.

    It appears that a square, about 24×24, 1-inch-deep filter filters in-coming air,
    which passes through a set of fins, which are very close above
    a pan that catches water, the “filtered” air is aspirated by
    a fan/blower that pushes the filtered
    air up
    into another set of coils(?) maybe? these i cant readily access it appears to me.
    Im told that the air is cooled as it goes over these coils.

    What can i do to see the inaccessible coils?
    the first, accessible set of coils seem to be clean
    as i can see all the fins and spaces between them…Thank you
    for any help and your time.

    • Bob Jackson July 25, 2011 at 7:24 pm - Reply

      Based on your description – “main boiler room … 40 yards away” you most likely have a “fan coil unit” that circulates a glycol & water mixture pumped from the chiller unit (a.k.a. “main boiler room”) to your condo. Are there 4 equal size insulated copper pipes going into your condo air handler unit? This is a sure indicator you have a fan coil unit. Two pipes are the chilled water supply & return for cooling; the other two are the hot water supply & return for heating. Since you see two sets of coils, I believe you have the 4 pipe system. (Some systems have only 2 pipes and the water flow is reversed for heating and cooling.) I also expect your monthly bill is the total cooling or heating cost divided equally by the total number of condos. That is, your monthly bill is always the same as your neighbors.

      The insulated cold water supply pipe coming from the chiller (boiler room) should be in the 44 degree F range as it enters your fan coil unit in the condo. The cold water supply copper pipe should be “beer can cold” and sweat with condensation when exposed to the room air, if not, this could be your problem. Perhaps you have a malfunctioning chilled water control valve on your fan coil unit? Or a bad thermostat, which signals the control valve to open and close allowing the chilled water to flow through the coils.

      Dirty coils could be blocking the air flow and need cleaning. Fan coil units are available in many different configurations, some fan coils look like residential air handlers, however I’m unable to provide specific guidance on how to access your coils. You might be able to Google the owner’s manual or parts diagram for your unit using the manufacturer name and model number for insights.

      My recommendation is to call a HVAC company to inspect your unit for a bad control valve, check the thermostat and condition of the coils. My bet is you have a problem with the control valve.

  17. Felice July 27, 2011 at 10:42 am - Reply

    “Jackson” Thank you for your understanding, info, insight…

    yes the unit in has two, insulated, about 2-inch pipes
    near the bottom of the hvac unit, that go into it…
    the blower fan works and comes on and off but
    it does it very many times. i believe because
    the air it’s blowing out is rather moist/humid, as i mentioned.

    it seems that the large blower/fan needs to be detached and
    above it i would be able to access the condenser or evaporation
    coils….monthly bill is included in the monthly condo fee
    The hvac unit is a “gw bohn heat transfer division”
    Again thank you for any insights and your help…

    • Bob Jackson July 28, 2011 at 7:02 am - Reply

      > it seems that the large blower/fan needs to be detached and
      > above it i would be able to access the condenser or evaporation coils
      I think your air handler (fan coils) are an updraft model similar to this diagram.

      > The hvac unit is a “gw bohn heat transfer division”
      GW Bohn is now owned by Heatcraft. You may be able to find information on your unit by searching their web site for your Bohn model number.

      Please post back when you determine the problem.


  18. Colt July 29, 2011 at 8:36 pm - Reply

    Finished with school, and just starting my HVAC career. This is a great site! I’m sure I will visit it again. Very informative. Thanks Bob.

  19. Felice August 1, 2011 at 10:03 pm - Reply

    do you think the problem
    is likely from the ‘boiler room’ …that
    the liquid from there is not cold
    enough? Thank you for your help.

    • Bob Jackson August 2, 2011 at 6:29 am - Reply

      A chilled water temperature problem (too warm) is unlikely, otherwise your neighbors would be complaining. As I wrote in my July 25 reply:

      “My recommendation is to call a HVAC company to inspect your unit for a bad control valve, check the thermostat and condition of the coils. My bet is you have a problem with the control valve.”

      To clarify, I believe you have a problem with the water control valve or the control circuitry (relay board) that operates the valve.

  20. Mike Maul August 2, 2011 at 11:32 am - Reply

    My coils are inverted compared to your photo. The inner part is very clean and water appears there. The outer part is dry and appears to have collected pieces of the insulation from the surroundings.

    Should I be using a cleaner on the outer dry part to improve circulation/performance?

    Very nice site with the best information I’ve seen. Thanks for making it available.

    • Bob Jackson August 2, 2011 at 11:33 pm - Reply

      I doubt the foaming coil cleaner will remove the bits of fiberglass insulation plastered to the upstream side (dry side) of the evaporator coils. Coil cleaner is a detergent and disinfectant that won’t break down fiberglass insulation mechanically wedged into the coil fins. What you need to do is get a new pump sprayer and direct a stream of very warm water from the far side (i.e. wet side) through the coils to knock off the insulation on the other side. (Don’t use a pump sprayer that’s had other household chemicals or pesticides in it or you’ll be breathing it later.) This isn’t “pressure washing”, rather it’s applying light pressure to remove the insulation. You’ll need to turn off the circuit breaker and place a pan under the coils to catch the water and protect the blower motor and other electronics from getting wet.

      If you’re *very careful*, a soft long bristle brush can be used to help remove the insulation. Go easy and check your progress because the fins are easy to bend/fold over.

      The next issue is to determine how insulation is getting blown onto the coils. Do you have a break in the plenum or ductwork? Has an insulation panel inside the air handler become loose? Is the air filter seated properly? The color and texture (pink, yellow, white, black; coarse or fine) of the insulation is usually a good indicator of where it originated.

  21. Mike Maul August 4, 2011 at 11:41 pm - Reply

    Thanks for the information. I’ll try what you suggested.

  22. Scott August 24, 2011 at 5:07 pm - Reply

    Great writeup. You have the refrigerant lines mislabeled on your photo. The cold (liquid) side coming in from the compressor should be the one wrapped in insulation. The gas return line should be the exposed copper line running back out to the compressor.

    • Bob Jackson August 24, 2011 at 7:54 pm - Reply

      > The cold (liquid) side coming in from the compressor should be the one wrapped in insulation.
      Nope, the photo is labeled correctly.

      The small copper pipe carries the relatively “hot” (or at least warm ~100F) high pressure liquid coming from the outside compressor/condenser unit to the air handler evaporator coils in the attic. See Figure 1.6 on page 8 and Figure 1.9 on page 10 of the “PRINCIPLES OF AIR CONDITIONING” as to why the liquid line from the condenser is hot in relative terms (100F).

      Also see “How does air conditioning work?” by Austin Community College. The small “hot” copper liquid line in question runs from the Condenser (#2) to the Metering Device (#3) in the Austin College diagram. The Metering Device is also known as an Expansion Valve which flashes the high pressure hot liquid refrigerant refrigerant to a low pressure cold (20F) gas for circulation in the evaporator coils. The larger copper pipe is the return refrigerant gas line that is remains somewhat cold after leaving the evaporator coils and must be insulated to avoid condensation and sweating all over the attic and inside the walls.

  23. Lisa F August 25, 2011 at 6:26 pm - Reply

    I live in a condo(all electric) and my downstairs neighbor got a bad leak. They came out and cleaned her unit and said it’s mine or the unit upstairs. My upstairs neighbor just replaced theirs and mine hasn’t been cleaned in several years. I have little money and I am very concerned. They said the water is coming from the condensation pipe that travels throughout out units. It serves us all.

    • Bob Jackson August 25, 2011 at 7:24 pm - Reply

      So, the neighbor below your unit had water damage and the repairman says the water damage was caused by a leaking condensate from one of the A/C units on the upper floors, and you believe your unit may be the cause? Clogged condensate drain pipes are a common problem.

      An HVAC repairman can usually fix this for the price of a standard service call. Dirt, slime and algae tends to build up in the condensate drain outlet and/or pipe, causing the drain to clog, water will overflow and run down between the floors and walls. Cleaning isn’t difficult – wipe away what’s visible, run a bottle brush instrument down the pipe, blow it out with compressed air, chemically disinfect/kill the algae and rinse out the pipe, then put some time release algae inhibitor tablets in the condensate drain pan for long term (couple of months) relief. Most condensate drain pipes are PVC plastic and worst case a section can be sawed out to get access at a clog further down the pipe and replaced.

      > They said the water is coming from the condensation pipe that travels throughout out units. It serves us all.
      If the HVAC technician says your drain pan and drain is fine, then take the matter up with your condo association as a common infrastructure maintenance responsibility.

      > mine hasn’t been cleaned in several years.
      Yours may need inspection and cleaning anyway. You’ll save money on the lower electric bills when the system is tuned up and running at optimum efficiency.

      Please post back when you find the problem and how it was repaired.

  24. Justin October 15, 2011 at 1:24 pm - Reply

    Huge help Bob, thank you very much. :)

  25. Jeff March 25, 2012 at 1:49 pm - Reply

    is there anything that can be sprayed on a/c evaporator coils to make water sheet down them instead of water dropping off before reaching drain pan?

    • Bob Jackson March 25, 2012 at 3:08 pm - Reply

      If your evaporator coils are clean the condensate should wick down to the condensate pan. Dirt or mold on the coils will interrupt the flow, soaking up water and providing sites for the water to drip off the coils before reaching the pan. Think of a dirt having the same effect as a stalactite on the roof of a cave.

      To your question, I’m unaware of a HVAC product – other than coil cleaner – that will repel water as your describe. Most coils are made of aluminum, which if clean won’t adsorb water to the extent that it beads up and drips off prematurely.

  26. rene June 24, 2012 at 5:25 pm - Reply

    Looking for advice about our a/c unit. It blows cold air but the house is not cooling. The temp in the house is 10-15 degrees higher than what it’s set on. The smaller uninsulated copper tube is hot to the touch. We’ve cleaned the filter and sprayed down the outside unit and blew the dust out of the indoor unit. Husband thinks it is just low on freon. I’m fearing it’s not that simple of a solution. It’s a Trane xr 80 and less than 10 years old. Feeling desperate and afraid of a huge expense. We live in Texas and it’s hot.

    • Bob Jackson June 24, 2012 at 9:40 pm - Reply

      Is the outside compressor unit and fan running? It’s normal for the small uninsulated copper tube to be hot to the touch – that’s your high pressure liquid line coming from the outdoor compressor that goes to the evaporator coils in the air handler.

      New Trane XR80’s have a 10 year warranty on internal parts, so your unit might also still be in warranty. Recommend calling a Trane-certified service technician. After the problem is diagnosed, he can tell you if it’s covered by the warranty or how much the repair will cost and your options. You’ll initially only pay for the service call (it typically costs less than $100) and can make an informed decision what to do next.

      Let me know when you find the problem.

  27. LBD July 6, 2012 at 9:13 pm - Reply

    This is great info. I knew the leak around my unit had do do with the evaporator coils but had no idea how to diagnosis or fix the problem. I really hope I can fix this!

  28. bob July 9, 2012 at 8:26 am - Reply

    I have 9 year old furnace/ air conditioner. About 4 years ago, they had to replace the a/c “A” coil due to a leak. Everything was fine for a year or 2, then we noticed the house humidity was going way up and the temp very slowly would drop. Tech checked system and said everything look fine, but also said something is not right. (?)
    There was a 14 degree difference between supply and return. said it should be 16 to 20. said refrigerant level was fine.
    This year, same thing, BUT now it seems like there is just not enough air blowing out of the registers. We change the MERV 10 pleated high capacity filter about 3 times a year. Manufacture recommends once a year.
    System looks clean, but the acess panel on the “A” coil is behing all the little valves, drier and small tubes, and the tech said you should not move them out of the way. He also said the inside of the “A” coil could be plugged up with dust, restricting air flow.
    We have several birds, and I dont want to use cleaners on the coils, since vapors can kill our birds.
    Can I just hose the “A” coil off?

    • Bob Jackson July 9, 2012 at 3:23 pm - Reply

      Reduced airflow and high humidity could mean your AC evaporator coils are dirty with mold/mildew growing on them. The only way to really know is to open up the air handler and inspect the coils.

      Did the AC technician inspect your ductwork and air handler housing for leaks? You could be blowing cold air through a break in the ductwork somewhere in the attic. Check if the air filter housing is sealed to prevent unfiltered air from being drawn into the air handler and clogging up the coils. (I cover the filter slot on my air handler with a piece of aluminum HVAC tape.) Also check if the blower motor fan needs cleaning.

      If you’re not comfortable opening up the air handler, hire an HVAC service company to clean the coils. Ask that they inspect the coils for dirt/mold first to see if this is the problem, then clean the coils with a pump sprayer and wand filled with a mild coil cleaner solution to shoot through the coils. You’ll need to move the birds outside and air out the house for 20 or 30 minutes with the windows open and the air handler running. Wait until any scent of cleaning fluid is gone before moving the birds back inside. The issue is the coils need to be disinfected to kill the mold/mildew so it doesn’t come back anytime soon.

  29. RMS July 20, 2012 at 1:31 pm - Reply

    Great info. I got the coils clean, and saw the comment above about the missing A frame cap. The AC works well, EXCEPT one duct that blows warm air. The duct is a single line into the distribution box (dont know what it is called) and I cant see or feel any leaks. With a thermometer I measured all other ducts air at about 60F, this one is at 80F! Could the missing cap be the problem? Anything else I should check for?

    • Bob Jackson July 21, 2012 at 9:10 am - Reply

      If the AC vent is located in the ceiling and you’re able to trace the branch duct line in the attic back to the main trunk, then one of the following must be the problem for the warm air:

      1. A damper is blocking the air flow. Dampers can be manually or electronically controlled.
      You will need to inspect the ductwork to see if there’s a damper that’s partially closed.

      2. There’s a break in the ductwork.
      Follow the branch line from the main trunk to the ceiling vent boot, looking for taped
      joints that have separated or holes in the duct (maybe a squirrel chewed a hole?).

      3. Something is blocking the branch line duct.
      It’s possible a piece of plenum or ductwork insulation came loose and is clogging
      the branch line. If the airflow is very weak and you’ve checked everything else,
      then separate the branch line from the main trunk duct and look inside.

      4. The branch line is excessively long and/or too small, and not covered by
      attic insulation. The cold air is simply heating up on it’s way through the
      ductwork. If the branch line is only 4 inches inside diameter, more than 20 feet
      long and laying on top of the attic insulation, then the hot air in the attic
      can cause the air inside the duct to heat up.

      I’m guessing the problem is #4. The fix is to replace the 4 inch ductwork with a 6 inch diameter branch line for increased airflow to the room. Cover the branch line with a fiberglass attic insulation to minimize the cooling losses to the hot attic.

  30. jsid July 22, 2012 at 10:08 am - Reply


    • Bob Jackson July 22, 2012 at 10:31 am - Reply

      See my comment dated September 14, 2011 at 8:08 pm in Part 2 for advice. Comments are listed in chronological order.

  31. jamie September 4, 2012 at 11:55 am - Reply

    I’m having trouble getting the access panel door off. My refrigerant gas line seems to be sealed to the access panel door with a round seal making it difficult for me to remove the panel. Is it okay to break this seal somehow?

    Here is a picture. If you zoom in, you can see the black seal.

    Thanks, Bob!

    • Bob Jackson September 4, 2012 at 7:27 pm - Reply

      The photo helps a lot. The black seal in question is just a gasket to seal around the refrigerant line where it enters the air handler to prevent air leaks and condensation. I see that you’ve already removed the right side access panel screws. Just wiggle the access panel up and to the right. The gasket is sticky from being in place for so long.

      BTW – the HVAC tech who installed my system neglected to install the foam refrigerant line gasket. I found my gasket in the plastic bag with the owner’s manuals. To limit the air leakage, I partially sealed the access panel opening with HVAC tape.

  32. jeff November 15, 2012 at 1:13 pm - Reply

    I did not look through all of the comments so maybe this was pointed out. You do not have a u-trap on your drain line. This allows air to be sucked back up the pipe, which is like srilling a hole in the duckwork, as well as “spitting” the water all over the place that is trying to drain.

    • Bob Jackson November 15, 2012 at 10:06 pm - Reply

      > Jeff wrote:
      > You do not have a u-trap on your drain line.
      Hi Jeff,
      The purpose of a U-trap is to prevent sewer gases from getting into the air handler and stinking up the house, this is why bathroom and kitchen sinks have a U-trap (a.k.a. P-trap). My attic air handler condensate drain line runs to the outdoors, not to the sewer line. Therefore a trap is not required.

      > Jeff also wrote:
      > This allows air to be sucked back up the pipe…
      The blower motor on my system pushes air into the evaporator coils as illustrated in the 2nd photo of the project. This creates a positive pressure in the coil box that will not “suck [air] backup the pipe”, rather it pushes air and condensate down the drain line to the outdoors.

      The condensate drain line is in the original configuration as the HVAC system was installed; I have not modified this.

      === Reply to Jeff’s 2nd comment ===
      > Jeff wrote:
      > One more thing. The incoming cold liquid line should also be insullated to retain the “chill”.

      What you describe as the “incoming cold liquid line” is incorrect.

      The refrigerant liquid line is very warm-to-hot as it leaves the outdoor compressor unit; a result of compressing a gas to a liquid. There is no “chill” on this side of the refrigeration cycle; place your hand on the copper tube and you’ll feel it’s quite warm. This is why it’s an uninsulated copper tube all the way from the outdoor compressor to the attic air handler because warm lines don’t cause condensation and sweating.

      The refrigerant liquid line was installed this way when the home was built and is the standard method of doing so; I have made no modifications or given advice to make changes to the liquid line in the project.

  33. jeff November 15, 2012 at 1:14 pm - Reply

    One more thing. The incoming cold liquid line should also be insullated to retain the “chill”.

  34. Andre Baran December 26, 2012 at 5:31 pm - Reply

    Question please for Bob Jackson,

    Sir, you published a picture of your air handler/evaporator coils back in 2009 and claimed that the unit was 9 years old. You pointed out the rust on the frame and some discoloration on the copper tubing. I had a Carrier unit installed 2 years ago and after about a year and a half started noticing rusting condensate coming out from my pvc drains. Looking inside I was shocked to see my 2 year old air handler look almost as rusty as your 9 year old one. I am worried that this is premature deterioration but my A/C company does not want to pursue it and claims that my cleaning of my drains with bleach may be partially responsible. Any ideas or suggestions? The unit is in my garage in Florida but my prior 14 year old Trane unit did not appear significantly more rusted than what I see now.

    • BobJackson December 27, 2012 at 12:58 am - Reply

      Hi Andre,
      Rusted end plates on evaporator coils are typical because manufacturers use steel for this part. The end plates are themselves are just supports for the copper tube and aluminum fin coil pack. I’m uncertain if the end plates rust because water condenses on the chilled metal and/or galvanic corrosion at work due to contact between dissimilar metals (steel end plates and copper tubes). I’m leaning towards water condensation being the main cause for rusted end plates.

      Rusted evaporator coil end plates are unfortunately common:
      * Rusty evaporator…anything that can be done to slow?
      * Excessive rust on evaporator coil?
      * 14 month old Trane rusting

      The above links are by HVAC-Talk.

      Rusted end plates don’t necessarily mean the evaporator coils are leaking refrigerant, especially if the aluminum fins and copper tube packs are corrosion free.

      Take a look at this slides 4 to 8 of this Evaporator Coil Assembly presentation for a general overview.

      Better evaporator coils such as the Trane All-Aluminum Comfort™ Coil feature all aluminum coils, including aluminum end plates and tubes. The inner coil panels are painted to resist corrosion and can be removed to access the inside of the coils for cleaning. This article illustrates the difference between the Trane All-Aluminum versus copper/steel coils after a 500 hour salt spray test.

      While I not owned a Trane All-Aluminum Comfort™ Coil unit, I had an old AC system at my former home in Florida replaced with a Trane XL 16i system and was very happy with it.

      If you want to do something about the rust on your evaporator end plates, paint the end plates with COLD GALVANIZE Corrosion Inhibitor. COLD GALVANIZE is very high in zinc which acts as a sacrificial anode, protecting the steel from rust. Turn off the AC system, open up the air handler to expose the coils, wait until the end plates are completely dry, be careful to protect the air handler cabinet and coil fins from overspray and apply the COLD GALVANIZE Corrosion Inhibitor, allow it to dry, then close up the air handler. I would only do this if your system is past the manufacturer’s warranty or before installing a replacement coil at your own expense. If your system is still under warranty, hire a licensed HVAC technician to do it for you if he says it won’t void the factory warranty. However, you will only be able to access the outside face of the steel end plate so it’s only addressing part of the rust issue.

      All said, I would let the rust be and buy a better designed system when the time comes.

  35. Scott March 18, 2013 at 4:48 pm - Reply

    I m about to clean my Evaporator Coil in my air handler unit as I think it is the cause of a very bad smell coming out of my AC vents.

    My question is:

    Why is this smell only evident when I turn on the AC? The heater has no bad smell when turned on and the airflow should be going over the same equipment. It is that the heater is blowing moist air over the coils and thus mildew and such is building up and when the coils are active in when the AC is on, that is when the smell gets permeated to the airflow?

    Thanks in advance.

    • BobJackson March 18, 2013 at 5:19 pm - Reply

      The bad odor is noticed when the AC is on because water condenses on the chilled coils, wetting the coils and condensate drain pan. Some of the condensate evaporates and is blown out the air vents, taking the bad smell/odor along for the ride. For an analogy, what smells worse: a dry or wet dog? :-)

      When you clean the evaporator coils, also check the condensate drain line is not clogged.

  36. Mark Robinette June 22, 2013 at 10:48 am - Reply

    Thank you so much for such an informative site!

    I’ve got a three year old system (in a 33 year old house). Past several months, my allergies have been off the chart. There is a progressively worse moldy odor coming from all registers every time the unit cycles. Was able to get the sheet metal front off the A coils and found the coils to look clean and the drain line is open. Went ahead and used some no-rinse coil cleaner I had on hand. Although tight quarters, I shined the light further up into the plenum and found that the fiberglass insulation that is glued to the walls of the plenum were wet and covered in mold!

    Was able to cut a scuttle hole in the side of the plenum, about 10″x20″. Covered the top of the A coils with a towel and used a large scraper to scrape the damp, molded fiberboard insulation from the sides of the plenum leaving it temporarily uninsulated. Wasn’t able to access the upper distribution box to see if that fiberboard insulation is damp also. I’ll save that for next weekend.

    Question – what on earth is causing the wetness inside the plenum box? I crawled the entire length of the attic, all ductwork is good. I don’t have any damper issues. All registers are blowing the same volume they always have. All ductwork is well insulated and no breaks or obstructions. I’m stumped!

    • BobJackson June 22, 2013 at 4:53 pm - Reply

      > Question – what on earth is causing the wetness inside the plenum box?
      Hard to be certain why moisture is condensing inside the plenum box. Just to be sure, mold was growing inside the plenum box and not the foil faced insulation inside the sheet metal coil case?

      Are you certain it was mold growing on the plenum duct board? The airstream surface of rigid duct board is often coated with a moisture resistant black mat, which could look like a dark mold layer on the yellow fiberglass substrate.

      The condensation may be caused by water droplets being blown off the evaporator coils, especially if the coils are partially clogged on the underside, or upstream side where it’s difficult to see, creating localized higher than normal air velocity in the unclogged areas. Wide rivers run slow, narrow rivers run fast (Bernoulli’s principle).

      Whatever is causing the condensation in the plenum box, the best way to deal with mold is:
      * Verify the evaporator coils are clean inside and out, and nothing is obstructing the air flow.
      * Check the humidity level in the home. If the humidity is greater 50% in the summer with the A/C running, then something may be wrong. It could be the A/C unit is over-sized (big blast of cold air, but doesn’t run long enough to lower the humidity), undersized (can’t keep up with the load) or the system needs a tune-up (low refrigerant, dirty compressor coils, dirty evaporator coils, etc). The EPA recommends less than 60% humidity in the summer to for comfort, limit condensation and mold.
      * If you see mold in the plenum box or evaporator coil case insulation, turn off the system and let it dry out. Spray down the moldy insulation surfaces with Lysol to kill the mold. Wait until dry, then vacuum the rigid duct board with a brush attachment. Take care not to touch the evaporator coil fins, which bend very easily.
      * To prevent mold from recurring, install a ultraviolet air treatment system in the plenum box. The UV light kills mold and bacteria.

      Also recommend calling a licensed HVAC technician for an expert opinion about your system, since every situation is different.

      This Honeywell UV Treatment System kills mold on evaporator coils and inside plenums:

      Product literature and installation guide: Honeywell UV100A1059/U Ultraviolet Air Treatment System.

      A reasonably accurate and not too expensive digital temperature and humidity hygrometer/thermometer:

    • BobJackson July 7, 2013 at 10:25 am - Reply

      Follow-up to my original reply on June 22, 2013 that suggested an Ultraviolet Germicidal Light (UVGI) to prevent mold growth. I liked the idea and installed a UV light coil treatment light in my air handler as detailed in this project.

      > Question – what on earth is causing the wetness inside the plenum box?
      Two additional thoughts: Make sure the plenum box is well insulated and the relative humidity is 50% or less in the house.

      Let me know if you’ve solved the problem.


  37. Yash June 25, 2013 at 1:30 pm - Reply


    My attic ac is not generating any water! ! ! I am not seeing any water drain to the pipe and I am also noticing that I am not having sufficient cooling at the second store of the 2 story house. I have technician checked the pressure and the freeon pressure is correct. Does this mean I need to clean the coil?


    • BobJackson June 25, 2013 at 6:14 pm - Reply

      Since the HVAC technician checked the refrigerant pressures, this means the compressor unit is OK; i.e. the compressor motor and circulation fan are operating properly.

      The HVAC technician didn’t inspect the air handler (evaporator coils, blower motor, condensate drain, electronics, etc.) while he was there?

      Since the compressor unit and refrigerant levels are good, do the following:
      * Inspect the air filter. If it’s really dirty, then it will block the air flow and the evaporator coils may ice up, hence the no condensate (not generating water). Change the air filter if has been changed in 30 days.
      * Turn on the AC for 30 mins.
      * Locate several air vents near the air handler. Is there a strong and cold air flow from the vents?
      If the air flow is weak, the evaporator coils may be dirty/clogged, you could have a bad blower motor or there could possibly be a large air leak in the duct work.
      * Turn off the AC at the thermostat.
      * Open the evaporator case panel.
      * Are the evaporator coils iced up or dirty inside or out? Use the flashlight and hand mirror technique to look through the coils for dirt/mold on inside the coils. Ice on the coils means there is insufficient air flow through the coils, which causes the coils to get too cold and ice up. The evaporator coils are a heat exchanger; the cold refrigerant inside the coils is warmed by the air blowing through the coils which prevents the condensate water from freezing on the coils; likewise the coils cool the warm air from the house.
      * While you’ve got the coil case open, check the condensate drain pan and drain pipe for clogs.

  38. Kasia June 27, 2013 at 5:18 pm - Reply

    Hallo Bob,
    I have a huge problem. My A/C stopped working last night. It is only 03:15 pm and temperature in my place is over 80.
    The unit is running outside but inside everything is dead silent. Please advise me ASAP. I am afraid that since I don’t know anything about A/C and don’t know any A/C techncian that I might be charged for something that does not need to be repaired. Would you have any idea what could cause my problem and how expensive could be the repair?

    • BobJackson June 27, 2013 at 7:28 pm - Reply

      If the indoor air handler isn’t working, check the following:
      * Check the circuit breaker; the outdoor compressor and indoor air handler are normally on the same circuit breaker, so it’s unlikely this is the problem but yours might be on different breakers.
      * There’s normally a secondary power shutoff switch by the air handler, it looks like a light switch mounted near the air handler. Check that it hasn’t been inadvertently switched off.
      * Has the condensate safety overflow switch been activated? Depending on the configuration of your AC system, it might be the condensate drain pump isn’t working (this happened to me) or an overflow switch on the gravity-flow drain pipe located near the air handler. However, if the safety switch is tripped then it should shutoff both the outdoor compressor and indoor air handler, so I doubt this is the problem.

      Otherwise, you’ll have to call an HVAC technician because the air handler blower motor, motor capacitor or control circuit electronics are bad.

      The cost of a service call to diagnose what wrong will be in the neighborhood of $80 to $150 (call around as rates vary). A bad blower motor capacitor would be the least expensive to replace.

      Meanwhile, turn off the AC until it’s repaired.

  39. Jim July 9, 2013 at 7:18 pm - Reply

    Hey Bob,
    We have some kind of leak from where the coils are stored. I’m not sure if a pan is broken or the drain pipes are blocked. The front panel on mine has a type of metal tape with some type of putty behind it. I’m afraid to take it off because I might damage the unit further. Should I have a air conditioner repairman come out or just try breaking it all down myself? How much do they usually charge to replace or repair something like that?


    • BobJackson July 9, 2013 at 7:43 pm - Reply

      Since you’re concerned about opening up the coil case yourself, I’d call the air conditioner repairman. Call two or three HVAC repair companies and ask what they charge for a diagnostic visit. My guess is between $75 to $150. The cost of the service call is usually credited towards the repair cost, if repair work is needed.

  40. Colin August 3, 2013 at 1:04 pm - Reply

    Hi Bob,

    Thanks for all the help. In addition to cleaning the evaporator coil I also needed to clean the blower fans. I took apart the motor, fan and housing and cleaned them all, but am running into trouble putting them back together. There’s no clearance between the fan and the housing when I screw the motor back into the housing, preventing the fan from moving freely. To make matters worse, now when I try to take the motor back out of the fan to realign, I can’t! It’s stuck. Am I missing something? The motor is a Dayton 3LU83G. Thanks in advance.

    • BobJackson August 3, 2013 at 4:14 pm - Reply

      What is the make and model # of your air handler? The air handler service manual is often available online which may have service instructions. Whatever you do, don’t force the parts together because it’ll make matters worse. You may need to call a HVAC tech to reassemble the blower unit.

  41. Anil August 17, 2013 at 8:51 pm - Reply

    Hi Bob,
    The drain pipe from my evaporator coil unit seems blocked causing condensate to be overflowing into the adjacent housing for the computer control/ motherboard and then dripping from the seams below. Unfortunately, I am unable to clean the drain pipe as the previous installer had glued a plastic elbow to the outside of the drain pipe and attempts at unscrewing have resulted in the entire drain pipe rotating freely without it coming off. If I am apprehensive of opening the unit and instead first try and cut the drain pipe to try and flush it clean, can I then get another piece fitted in to allow drainage and how would I be able to do so? Will that necessitate opening the coil unit anyway? A tech. I had called said that it would require the entire coil to be changed as rusting of the collection tray inside would have caused the drain to block. Can just the collection tray be changed?

    • BobJackson August 18, 2013 at 10:49 am - Reply

      > Unfortunately, I am unable to clean the drain pipe as the previous
      > installer had glued a plastic elbow to the outside of the drain pipe
      The AC evaporator coil condensate drain (or “drip pan”) typically has a 3/4″ MPT (Male Pipe Thread) PVC connector. MPT fittings are also known as National Pipe Thread (NPT), which just means it’s a standard threaded fitting available at home improvement stores.

      The threaded end of the 3/4″ PVC MPT fitting screws into the condensate drain pan (hand tight only!) and 3/4″ PVC drain pipe is glued (solvent welded) to the other side of the fitting. You can see the 3/4″ PVC drain line fitting at the lower right of this photo.

      See Figure 2 on Page 3 of these evaporator coil installation instructions for a representative condensate drain pan connection diagram.

      > and attempts at unscrewing have resulted in the entire drain pipe rotating
      > freely without it coming off.
      You’ll need to remove the evaporator coil case access panel to see the other side of the condensate drain pan connection. If you have a metal drain pan without a factory made drain adapter (molded plastic module) there’s may be a hex nut and rubber washer inside the drain pan that’s spinning and preventing you from unscrewing the 3/4″ PVC MPT drain fitting.

      > If I am apprehensive of opening the unit and instead first try and cut the drain pipe to
      > try and flush it clean, can I then get another piece fitted in to allow drainage and how
      > would I be able to do so? Will that necessitate opening the coil unit anyway?
      Opening the coil case to see what’s preventing you from unscrewing the 3/4″ threaded drain fitting is necessary to figure out if:
      * A threaded nut spinning inside the drain pan is preventing removal of the threaded drain fitting.
      * If the drain pan connector is possible broken.
      * What’s clogging the drain line. Rust, dirt, mold or other debris.
      * If you have a severely rusted and leaking metal condensate pan.
      * Condition of the AC evaporator coils.

      Should the 3/4″ PVC drain pan fitting need to be replaced, you’ll probably find it easiest to saw the PVC drain line a foot or so downstream of the evaporator coil case to remove the threaded drain pan fitting and elbows because there may not be room to install a 3/4″ PVC straight connector at the elbow. The repair consists of gluing on a 3/4″ PVC straight connector on the old pipe where it was cut then measuring and installing new pipe, elbow(s) and threaded drain pan fitting to match what was removed. The cost of the PVC pipe and fittings is less than $20. The PVC purple solvent/cleaner and glue is maybe $10 or $15. If you search this site for PVC (see top right of the page for the search box) you’ll see many examples of PVC plumbing projects.

      > A tech. I had called said that it would require the entire coil to be
      > changed as rusting of the collection tray inside would have caused the drain
      > to block. Can just the collection tray be changed?
      A metal drip pan can rust which besides blocking the drain line will also leak onto the furnace and blower motor, eventually filling up the secondary drain pan causing the safety cutoff float switch to activate and shut down the unit to prevent flooding.

      The collection tray (drip pan or condensate drain pan) can be changed, however it requires draining the refrigerant, cutting the copper refrigerant lines and removing the evaporator coils. The work costs hundreds of dollars and at that point, it’s probably cost effective to replace the AC evaporator coils with a new & improved unit. I’d go with a “cased coil” unit meaning it’s a complete insulated sheet metal coil case and evaporator coils. My A/C unit is the “cased coil” type. An uncased coil is just the A-frame coils and drip pan assembly.

      You can send photos of your unit to bob (at) if you’d like additional advice.

      Recommend you have an HVAC tech take a look at your unit. A service call usually runs $75 to $85 and he can tell you what’s the problem, clean the drain line and make PVC drain line repairs which usually aren’t expensive for what you described. The HVAC tech will also have special drain line suction equipment to remove any downstream clogs. If your drain pan is in really bad shape, he can provide a replacement estimate so you can budget for the work.

  42. Kathy March 27, 2014 at 7:25 pm - Reply

    I’ve had issues with my HVAC system since moving into my house, which was built in 1998, although I’ve lived in it 5 years.

    I live in a suburb of Phoenix, Arizona, so run the air conditioning for many more months than I would living anywhere else. I am sure there are leaks in my flexible ductwork, in addition to other problems, but the ducts are located in the attic and I cannot find a single HVAC company that will check them.

    While every company I’ve talked to, about 10 of them over the years, wants to sell me a new system and an air cleaner, etc., not one seems to be concerned that my air handler has no drain line (I don’t think they know what it is), and that in the part of the inner flex ductwork I can reach when I take off the grilles/vents, there appears to be a black powder — like soot — even though I have no fireplace. There’s a lot of it stuck in the folds of the flex duct, so I don’t think a duct cleaning would remove it.

    I just don’t know what to do. Would you happen to know of any honest people or companies in my area? Should I just ignore it? Move? I planned on having this house for the rest of my life, but with filters full of gray and black “dirt” when I change them monthly, I’m not so sure.

    • Bob Jackson March 27, 2014 at 9:22 pm - Reply

      > not one seems to be concerned that my air handler has no drain line
      An air conditioner not only cools but also removes moisture from the air to lower the humidity. The moisture in the air condenses on the cold evaporator coils and a condensate drain line is required to take away the water from the drip pan. If your A/C system really doesn’t have a condensate drain line (gasp!), that black powder could be dried mold that’s blown off the evaporator coils and settling in your ductwork.

      > Would you happen to know of any honest people or companies in my area?
      You can find reputable air conditioning service companies on with uncensored consumer reviews. Best of all, is free and doesn’t require an account. For example, a search for “air conditioning repair” in Phoenix, AZ lists several good candidates.

      Call two or three A/C Service companies, explain the problem and that you want them to:
      * Perform a regular A/C system maintenance: Check the electronics, motor start capacitor, refrigerant charge, temperature drop across the evaporator coils, change the air filter, check the safety cutoff float switch, etc.

      In addition confirm that you want them find the source/cause of the black powder:
      * Verify your system has a condensate drain line and the line is not clogged.
      * Unclog and flush the drain line and drip pan if needed.
      * Open the evaporator coil case and clean the coils.
      * Check the attic supply and return ductwork for breaks and leaks.
      * Find the cause of the black soot; whether it’s mold or dirt from unfiltered air being drawn in from a break in the ductwork.

      Follow the HVAC technician around and ask questions. I had my A/C system serviced today and the tech was more than happy to answer my questions, show me the capacitor test readings, look inside the system, show me the gear he has in the van, explain why the humidifier control was wired incorrectly (he corrected it), various repair costs, upgrades and options. Most techs take pride in their work and enjoy when someone takes an interest. Just be nice and give the tech space to work.

      You might consider the 5-Minute Home Mold Test kit on a sample of that black powder:

      Let me know when you fix the problem.

  43. Kathy March 28, 2014 at 8:33 am - Reply

    Thank you so much for all this great information, Bob. I think a big reason that guys from the various HVAC companies are reluctant to check the ductwork and air handler is because they are in the attic. The air handler is easy to reach and to see and I have asked many of these guys about where the pan is and whether there is a drain line hidden somewhere that should be drained and they just tell me that this air handler doesn’t have anything like that.

    They treat me like I’m really stupid, but I have done more research on these split units and various parts and connections, etc., than it seems they have.

    I have a split system, with the compressor unit outside. I don’t know if that makes a difference.

    Anyway, thank you again for replying so quickly. If you like, I can update you (so you can update readers) on the companies I find and if any of them know what I’m talking about. If there isn’t any company in Phoenix that can do what is required, then that’s a huge business opportunity out here for someone who can.

    Thanks again.


    • Bob Jackson March 28, 2014 at 8:45 am - Reply

      What is the make and model # of your air handler? The manufacturer installation guides can usually be found online. While you do live in an arid desert climate a condensate drain line is still needed. Your split system configuration with an indoor air handler and outdoor compressor unit is very common.

      It shouldn’t be a problem having the A/C service company do a proper inspection and crawl around in the attic if you specifically make the request. You should expect to pay more compared to a routine service call.

      Please do write back when you find a company you’re happy with and resolve the problem. I’m always happy to give a shout-out to a job well done. You can also post feedback on their page.


  44. Dylan April 24, 2014 at 3:11 pm - Reply


    Long time reader, first time poster.

    My wife and I just moved into a new place. We have a Goodman company lp – AWUF180816AA hvac unit. The previous tenants used a lot of carpet powder and it got into the ac coils / heat exchanger. It’s causing air quality issues, so I’m trying to get it fixed up before summer.

    I tried using the foam cleaner from HD on them but it didn’t solve the problem. I’m wondering what my next move should be. If there’s a good, green way to clean them or if I need to hire a pro to take them out and clean them or even replace them. The ac unit is about 10 years old. I can add a link to a picture if that helps.

    Thanks and great website,


    • Bob Jackson April 24, 2014 at 5:53 pm - Reply

      Hi Dylan,
      I’d start with a professional carpet cleaning to remove the carpet powder. The next step is find out what’s been contaminated by the powder.

      Remove the grills from several supply and return vents in the carpeted rooms. Swipe your finger inside the duct; do you see and smell carpet powder? If so then duct cleaning may be necessary – I’ve no experience with duct cleaning and can’t vouch for it’s effectiveness; best to ask for customer references. You could try cleaning and if that doesn’t work think about replacing the ducts. The idea is powder inside the ducts will continue to cause an odor and be pulled into the air handler. Here’s a photo of a really dirty flexible duct that feeds the return air plenum upstream of the air filter. Hopefully your ducts are not so dirty. I recently replaced my flexible trunk ducts with sheet metal and the flex ducts had only a light amount of dust inside after 10 years of service.

      If the carpet powder is on the evaporator coils and electric heater, then it’s also on the blower fan, air handler interior surfaces, plenums and inside the ducts. The Goodman AWUF Series Wall-Mount Air Handler looks like it’s easy to service with two removable service panels. You should be able to inspect the blower fan after removing the upper service panel. (Take care to turn off the electricity at the circuit breaker first.) If the carpet powder is inside the blower fan unit, you’ll want to have an HVAC technician remove and clean the blower because there’s a lot of electronics in the way and it’s not a simple task. Ask the HVAC tech to clean the evaporator coils, too.

      The electric heating element on the Goodman AWUF Series is a thick rope-style loop assembly so I don’t think the carpet powder would be much of an issue here. The heating element is located above the blower fan on your air handler. If you decide to have the blower removed it’ll be easy to vacuum off the heater.

      Let me know what happens.


  45. Dylan Allen May 24, 2014 at 9:09 pm - Reply

    Well, it turns out carpet powder may not have been our biggest problem. It wasn’t on the duct vents or the blower.. I think the problem might be mold. On further inspection, the drain hose is filled with mold and the coils are still filthy after being sprayed with coil cleaner several times. . After spraying the coils with cleaner our landlord is done helping us fixing it so we’re trying to figure out what to do next. The drain hose doesn’t look to hard to replace, but I’m not sure where to get one.. Any help is appreciated. Thanks,

    • Bob Jackson May 24, 2014 at 10:32 pm - Reply

      Did you clean the evaporator coils with the aerosol foaming spray? Have you looked through the coils with the flashlight and mirror to see if their blocked with mold?

      If so, try the Heavy Duty AC Evaporator Coil Cleaning with the pump sprayer. If that doesn’t work then you may need to call an AC Service company. If the HVAC technician says the coils must be removed ($$$) for proper cleaning or replaced ($$$$) then it’s your landlord’s responsibility to fix it. Get a written report and estimate for your landlord. I’m a bit surprised your landlord isn’t pursuing the system maintenance, but then again… landlords.

      Drain hoses and PVC drain lines are easy to replace. Take care the drain line configuration is not changed; for example if there’s a P-trap don’t change it to a straight pipe section. Photos of your condensate drain lines would be helpful for specific advice. E-mail photos to bob (at)

      Also see this comment that describes the Mighty Pump™ A/C Condensate Drain Line Pump.

      Hope this helps.

  46. Aimee July 12, 2014 at 4:30 pm - Reply

    Hi, Bob. I have a question. Just cleaned the condensation pan on an a/c furnace because it smelled mildewy when I ran it. Put it back, turned it on, and it was good. About a half hour later the the unit stopped working and hasn’t turned back on since. I made sure the thermostat was on and tried the circuits. Any ideas what could be wrong?

    • Bob Jackson July 12, 2014 at 5:18 pm - Reply

      An overflow safety cutoff float switch may have been activated because the drain trap is clogged with dirt or maybe it was bumped?

      Depending on your A/C system configuration there may be a condensate pump, safety float switch on the drain line trap and/or a switch in the secondary drain pan beneath the air handler.

      Check the condensate drain line for a connection with two wires and that will lead you to the float switch. You can e-mail photos to bob[at] if you’d like me to take a look.


      • Aimee July 12, 2014 at 7:42 pm - Reply

        Thanks for getting back so quickly! So I checked into it. The float switch seems to be okay. Added water to the tray and it started emptying it normally. There is no flashing LED light in the furnace, though. I checked the breakers and they are working fine, which in turn allowed the float switch to turn on. The furnace switch is on as well. Thermostat is working, too. Attempted to switch to heat and still no signs of life. I had the motor replaced 4 months ago. I know it’s a long shot, but is there anything I can do to bring it back to life, or do I need a professional? Thanks!

        • Bob Jackson July 12, 2014 at 8:03 pm - Reply

          > Just cleaned the condensation pan on an a/c furnace because it smelled mildewy
          > when I ran it. Put it back, turned it on, and it was good.
          We’re talking about the evaporator coil condensate drain pan, correct? Most pans are not removable so I’m not sure what you “put back in”. What is the make and model # of your furnace and evaporator coils?

          > Attempted to switch to heat and still no signs of life.
          Something else to check is the cutoff switch behind the furnace access panel to access the electronics. It’s a spring loaded switch that flips out when the panel is removed. You might not have fully seated the panel and closed the switch, preventing the air handler from running. Normally the front panel simply lifts up & off with no screws.

  47. Allan Davis July 14, 2014 at 6:11 pm - Reply

    Hi Bob,

    My central A/C is Lennox and around 30 years old I believe. It has remained very effective in cooling my house, but the cool air has a strong mildew odor, so I can’t use the unit. I thought about the possibility of the evaporator coil being the source of the smell ( also considering the drip pan and the ducts ( though the smell is not there when the ducts conduct heated air)). Unfortunately, there was no access panel to the evaporator coil, so I had to cut through the plenum on one side, making a 12 x 6 inch hole. What I saw when I opened the newly cut panel was the outside of one side of the A frame with the fins in pristine condition without any signs of mildew or clear signs of the telltale odor. I could not see the coils as there is a triangular shaped piece that covers the front of the A frame. A strip attached with a few screws runs around this triangular cover, which may be what attaches it to the A frame. Removing this triangular piece, if even possible, would be fairly difficult and would involve cutting an additional hole in the other side of the plenum. My question is that given that the outside of the A frame is clean and without noticeable odor, may it still be the inside of the A frame where the problem lies. Is it inside the A frame where most of the focus of the cleaning is usually done? My other question regards whether you’ve seen this type of cap over the A frame and how to best deal with it. Thanks!

    • Bob Jackson July 14, 2014 at 7:33 pm - Reply

      Hi Allan,
      The exterior coils can look clean while the interior (or upwind side) of the A-frame evaporator coils will catch more dirt and debris, providing a medium for mildew to grow on. It wouldn’t be surprising to have a problem on a 30 year old system that’s been sealed and never cleaned.

      > Unfortunately, there was no access panel to the evaporator coil
      Do you have a cased or uncased coils? Cased coils are set inside a factory-made sheet metal box like mine. Uncased coils are inside a rigid ductboard box that’s typically fabricated on-site during installation. Ductboard is easy to cut and reseal with HVAC tape.

      > My other question regards whether you’ve seen this type of cap over the A frame and how to best deal with it.
      How to Clean Inside of AC Evaporator Coils should be helpful.

      Let me know if I’ve answered your questions.

  48. Allan Davis July 15, 2014 at 12:15 pm - Reply

    Hi Bob,

    Thanks for your reply. My system has uncased coils. From the 12 x 6 inch hole that I made in the plenum I see that it would require removal of most of that plenum panel to access and remove the cap that lies over the front of the A frame so to directly inspect and clean the upwind side of the coils.I would need to cut a new panel to screw in place over the big hole when I was done cleaning. As a possible alternative, I wonder whether merely spraying disinfectant through the downwind fins on the one exposed side might be adequate in killing the unseen mildew growing in the interior of the A frame. I can also make a small hole in the cap to put the nozzle of a sprayer through to directly spray disinfectant into the upwind side. I know it would be a temporary fix since the coils would not be cleaned with this approach, but I’d be happy with something that would last 1.5 months with the procedure to be repeated as needed and next year. If this is worth trying what disinfectant would you recommend I try? Would a dilute bleach mixture be okay?

    • Bob Jackson July 15, 2014 at 10:05 pm - Reply

      > I wonder whether merely spraying disinfectant through the downwind fins on the one exposed
      > side might be adequate in killing the unseen mildew growing in the interior of the A frame.
      It’s certainly worth trying. Mixing the cleaning solution with hot water helps, too. Have you tried the flashlight & mirror technique to see through the coils to determine if they’re block on the inside with dirt? A telescoping mirror is a big help.

      > Would a dilute bleach mixture be okay?
      Bleach is mainly a disinfectant whereas a detergent + disinfectant is better. Use a “no rinse” evaporator cleaning product like Nu-Calgon Evap-Powr-C because bleach doesn’t contain detergents and surfactants to lift and wash off the dirt. Bleach is also more difficult to rinse off and if absorbed by dirt/mold inside the coils can cause a long lasting odor (and potential breathing problems) compared to a no-rinse cleaner. Removing the dirt is important so the mold causing the gym sock odor doesn’t have a medium and food source to grow on.

      > From the 12 x 6 inch hole that I made in the plenum I see that it would require removal of most
      > of that plenum panel to access and remove the cap that lies over the front of the A frame so to
      > directly inspect and clean the upwind side of the coils.
      If cleaning the outside of the coils doesn’t product satisfactory results, cutting open the rigid ductboard evaporator coil case isn’t difficult but I recommend most people call an HVAC service and repair company since it’s an advanced skill level job.

  49. Ramiro Hernandez November 26, 2014 at 1:31 pm - Reply

    three years ago i replace the old air conditioner and since then i have had lots of problems with the new one.The first time was service was added Freon and the second and the third also, finale they told me that they have to replace the Evaporator Coil and i paid $ 450. i think that they use the old evaporator coil. will be hard to prove it, when they brought it down seems to me older than three years.I copy the labels on the on the old one. Serial No 6011B20283 Model CH362C6 Advance Distributor Products
    Please advise me.Thanks.

    • Bob Jackson November 26, 2014 at 6:51 pm - Reply

      The replacement air handler was manufactured in February 2011 based on the Serial No 6011B20283, where “11B” indicates 2011 and B is the 2nd month of the year according to this reference. It appears your HVAC company did install a new coil about 3 years ago.

      Or you can call Advance Distributor Products Customer Service at (800) 848-2270 and ask them to confirm the date when the replacement evaporator coil was made given that Serial Number.


  50. darleen January 4, 2015 at 5:04 am - Reply

    I have a fitizu Getting musky smell from split air condictioner how do I fix it-

  51. John Fitzpatrick March 2, 2015 at 7:46 pm - Reply

    A/C Tech installed a UV light to kill bacteria near coil. Blue light from unit emits into room through the air filter. Creates a faint blue tint on A/C screen. The light itself is not in direct view – only the glow from it’s being lit. Does this pose any danger to eyes or skin? Any information would be greatly appreciated! Thank you very much.

    • Bob Jackson March 3, 2015 at 8:01 pm - Reply

      The American Air & Water UV Light Frequently Asked Questions states:

      “Few materials, (primarily polished aluminum and magnesium oxide) effectively reflect UVC. The common mirror will not.”

      The American Ultraviolet Frequently Asked Questions entry for “What safety precautions should be taken when using germicidal UVC?” also states:

      “In personal protection applications (the use of lamps for room irradiation in homes, schools, offices, etc.), indirect fixtures such as TB and Corner Mount fixtures are mounted above eye level. Only the upper air is irradiated and persons or animals occupying the area receive no direct exposure.”

      Given the “faint blue light” you’re seeing through the air filter it’s indirect, reflected and safe. Still I would be mindful of not letting small children stare at it as it does look really interesting.

  52. Chuck erwin March 26, 2015 at 11:02 am - Reply

    I have a Trane XE80 it works fantastic, but lately I have been getting a lot of dust in the house.we had the duct work cleaned out by professionals.i can dust the house today and 2 or 3 days later I have to do it again what can you recommend thanks

    • Bob Jackson March 29, 2015 at 11:43 am - Reply

      Air duct cleaning typically uses a rotating brush attached to a high-powered vacuum hose. A thorough cleaning includes the air handler including the blower fan, fan housing, coils, supply & return plenums. Given the often complicated ductwork arrangement with 90 degree bends and intermediate distribution boxes that a cleaning hose can’t navigate some, areas will be missed.

      See Should You Have the Air Ducts in Your Home Cleaned? by U.S. Environmental Protection Agency for more information.

      The possible reasons you’re having dust blown into the house are:
      * The duct cleaning knocked the dust loose but didn’t completely vacuum it out.
      * Ductwork is often poorly installed with taped joints that come loose over time. The duct cleaning tool may have opened a return air joint that’s sucking in dust.

      My flex duct had a light dust coating after 12 years of service when I replaced it with sheet metal duct. This is normal and not worth cleaning because the dust sticks well to the flex duct. It’s also a challenge to thorough clean all those folds and ridges.

      A friend bought a 30 year old house with very poorly installed ductwork. Loose joints everywhere, including the at the return air plenum which was filthy. The excessive white dust inside the return air flex duct suggests they were sanding drywall with the air conditioner running. The solution was to replace the attic ductwork, supply and return plenum boxes.

      If I had seriously dirty ductwork, I would:
      * Determine why it was so dirty and what was allowing dirt to enter the system.
      Fix any loose joints, seal the air handler and keep up with regular scheduled maintenance.
      * Replace exposed ductwork rather than clean it.
      * Clean only short sections of ductwork that can’t be replaced such as wall stacks (duct inside the walls).

      So back to your dust problem:
      * I suggest opening up a couple of ductwork joints in the attic or crawlspace to see if it’s clean or dusty.
      * Inspect the ductwork for breaks or loose/leaky joints.
      * Inspect the air handler, supply and return plenums for cleaning needs and ensure it is thoroughly sealed.
      * Check the air filter to see if it’s dirty and/or getting dirty faster than normal.


  53. JC May 14, 2015 at 7:28 pm - Reply

    Great information!

    My question is “AIR FILTER RELATED”

    My Air handler has to openings for air filters
    1 has a cover the other doesnt(which is where the air filter is)

    Should i seal the opening with duct tape, and put air filter in other slot with the cover.
    Or do both slots need air filters
    I cant add a picture to show it better

    • Bob Jackson May 15, 2015 at 11:42 pm - Reply

      If I follow your description correctly, you have two air filter slots:
      Slot #1 is covered with no air filter.
      Slot #2 is not covered and has an air filter.

      You may have a multistage filter system, especially if the two filter slots are different widths (thickness). The 1st air filter would be a regular air filter to catch the large dirt particles and the 2nd filter (downstream) is intended to be an electrostatic model for the really small dirt. Electrostatic filters are typically the thicker than standard air filters. When the home is sold the AC User Guides are lost/misplaced and the new owner’s don’t know the original filter specifications and simply install just the one regular air filter.

      Do you see any manufacturer labels on your air filter unit? Then you could look it up on the manufacturer’s website.

      > should i seal the opening with duct tape…
      I always seal my air filter slot with metal foil HVAC tape which is a totally different product than “duct tape”. This eliminates the minor amount of unfiltered leaking around the air filter slot.

      > and put air filter in other slot with the cover?
      I don’t recommend installing a 2nd standard air filter because it can strangle the air flow and reduce your AC system efficiency. You’ll need to identify the correct type of air filter for the 2nd downstream position per the manufacturer’s specifications.

  54. Ron S June 10, 2015 at 7:10 am - Reply

    I had a tech come out and look at my central ac unit for a spring tune up. When he looked in the air handler the side of the evaporator coil facing the intake had mold. He stated that since it was so bad, he could not clean it for fear of disturbing it. He also stated that using a spray foam cleaner would not take care of it and that the mold would likely cake up between the fins and completely clog the unit. His solution was to replace the evaporator. Will a no rinse foam cleaner remove mold without moving it through the evaporator fins to clog it? Also if a rinse is used, is it possible that the mold will be passed through the evaporator to the discharge side and send the mold into the duct work? Any info would be greatly appreciated.

    Thank you.

    • Bob Jackson June 10, 2015 at 10:53 pm - Reply

      You’ll need to use the method explained in How to Clean Inside of AC Evaporator Coils to remove caked on dirt and mold. Purchase the professional cleaning solution, pump sprayer, fin comb and brush. Be patient and work carefully. It will require several cleanings and 2 or 3 hours time. Use the flashlight and mirror to check between the fins for blockages.

  55. Duane Moore June 14, 2015 at 2:20 pm - Reply

    This is awesome! Thank you so much. The guy I had come out tried to sell me an entire system for 10k, seriously. I’m in Orlando and worked some construction with some HVAC guys a lifetime ago and knew better. Unfortunately by Dad was just had in The Villages, FL for a whole new system and his house is only 10 years old, they are getting everybody over there. Just wanted to say THANKS! This stuff is easy when your properly instructed…you got a youtube channel?

  56. Michael June 14, 2015 at 11:52 pm - Reply

    I have a brand new unit and it is blowing hot air. The tech came out 2 weeks ago and put more frigate in it due to we got it in the spring. Now two weeks later and it is hot again. I looked at the A coils half are wet and half and dry, I have looked at everything he did before. He said there was no leaks. The unit is running, but never gets below 8 degrees of the outside temp. This is a 1350 sq ft house with a 2 1/2 ton unit. the large pipes are cold and sweaty. the small are warm. Outside unit has not shut off for 2 weeks. Help

    • Bob Jackson June 15, 2015 at 10:08 pm - Reply

      Wouldn’t a brand new AC system be under warranty? 2-1/2 tons for a ~1400 sq ft house is a reasonably sized system. A too low refrigerant charge will often cause the coils to freeze over but your coils are half wet and half dry. Since the last technician topped off the refrigerant charge and said there’s no leaks his findings are likely accurate.

      I’d call a different HVAC service company for a complete system checkup. The problem shouldn’t be hard to find. Verify the high & low side condenser (outdoor unit) operating pressures, compressor current draw, temperature drop across the evaporator coils, blower motor, etc.

  57. Paul June 22, 2015 at 11:25 pm - Reply

    I have a heat pump situated outdoors, with a Goodman Mfg. vertical air handler, model # “avptc30c14aa” in my basement. This new system was installed two years ago. The air handler’s coils occupy the lower half of the unit, and circuit boards are in the upper half of the unit. The air handler is fitted with a clean low cost air filter, located in the bottom of the air handler. This system seems to be cooling well and blowing lots of air out of the vents. But, as of a few days ago, the air handler began emitting a short duration, high pitched sound every 15 minutes. In addition, while the unit is idle, when I look into the air handler’s one inch diameter glass covered peep hole, located in the circuit board area (upper area) of the air handler, I see two red zeroes, one above the other, consecutively flashing. They continuously flash in the following order: first the upper zero lights for ~ 0.5 seconds, followed immediately by the lower for ~0.5 seconds, then darkness for ~0.5 seconds. The display changes when the air handler is running. So, while running, one sees a flashing green dot just to the left of a constantly lit, non-flashing red capital “F”. The green dot flashes 7 times every four seconds, then goes dark for one second, repeating this flashing cycle continually. Meanwhile, the red capital “F” remains lighted and does not flash. Would you happen to know what these diagnostic codes mean?
    Thank you for any time you might give to assisting me with this problem.

    • Bob Jackson June 23, 2015 at 9:00 am - Reply

      Per the AVPTC**14** Installation & Operating Instructions (which matches your AVPTC30C14AA model #) the communications circuit board has a 7 Segment Diagnostic LED for fault codes and a Green CFM LED next to it. CFM means Cubic Feet per Minute. See the circuit board illustration on page 13 of the above manual.

      The Green CFM LED flashing once for every 100 CFM of airflow. 7 flashes indicates 700 CFM, which is a reasonable volume of air.

      The 7 Segment Fault & Diagnostic LED Codes are listed in the Troubleshooting chart starting on page 23. Page 27 identifies a Code F as “Fan Only”. You’ll need to ask the HVAC technician if this is a normal or problem condition because the manual doesn’t provide additional information.


      • Paul June 24, 2015 at 9:19 pm - Reply

        I goofed. False alarm. It was not the air handler, it was “the verizon fios connector wall box thingy” located just 10 feet from it. This I discovered as I was standing one foot in front of the verizon box when it emitted the high pitched beep. My mistake?: I didn’t turn off everything else that could go beep in the night. If I had, I would have realized the beep was not comming from the air handler. … Pluus, I need to get my ears checked: … I could have sworn the beep was comming from the air handler!

        Thanks for your prompt answer.

  58. Michael September 10, 2015 at 3:59 pm - Reply

    Hi Bob,
    Thank you so much for your time in providing all of the very detailed information. I have an air handler unit in an apt building only 18 mo old where mold is growing on the evaporator fins. The bracket holding the filter in place seems to be creating a dam blocking the water from flowing smoothly into the drain pipe. The drain pipe itself is raised approximately 1/16 above the level of the pan. This leads to a constant layer of water in pan. Is it normal to have water in the pan? Secondly, could you help me understand the role of the damper. I live in Florida with high humidity in the summer and my thought is that the damper would be closed in those conditions. But I’m not sure at all about how to use the damper. I am planning on doing the cleaning with the foam cleaner. And I am also thinking about using a mold blocker like con chrobium, a sodium carbonate alkali (ph11) . Is this okay for using on the fins and evaporator ? Thanks.

    • Bob Jackson September 12, 2015 at 10:54 am - Reply

      I’d need to see a photo of the air filter bracket that’s blocking the condensate pan because that’s not right. Maybe it was installed incorrectly?

      > The drain pipe itself is raised approximately 1/16 above the level of the pan.
      Yeah that’s typical and it’s the same on my air handler. You’d think the manufacturer would have designed the drain such that it’s flush with the bottom the pan to prevent the shallow pooling. Drop in some condensate drain pan tablets to prevent algae from growing in the pan and drain tubing.

      > could you help me understand the role of the damper?
      In general a damper is a device to restrict or redirect the airflow within ductwork. Where is your damper located? It is manual or electronically controlled?

      You can e-mail photos to bob[at] – replace the [at] with the @ symbol.

  59. RD October 4, 2015 at 2:00 pm - Reply

    Hi Bob
    Just cleaned my AC coil evaporator with frost king foam cleaner. did a good job but I’m still getting water drips…could the coil evaporator (drip pan) at the bottom of it be clogged?
    Please let me know
    Thanks much for your help

    • Bob Jackson October 4, 2015 at 2:22 pm - Reply

      If the condensate drain is clogged you’ll see standing water in the drain pan when you remove the front panel of the evaporator coil case. Is the pan full of water and overflowing?

      Where exactly is it dripping water? Have you shined a flashlight through the coils onto a small mirror to check if the interior side of the coils are dirty? Normally the condensate water will wick down the face of the coils into the condensate drain pan. However, if the interior coils are dirty and “hairy” the water will drip off prematurely and fall inside the air handler. See How to Clean Inside of AC Evaporator Coils if the coil interior is dirty.

      • rd October 5, 2015 at 6:47 pm - Reply

        Thank you!…I looked at coils on top and were somewhat dirty so I proceeded to foam clean. water seems to stop. A bright flashlight did the trick, so far it’s looking good.
        You’re the best!
        Best Regards

  60. Bing Dong July 25, 2016 at 12:02 pm - Reply

    Hi Bob,

    Can this apply to the indoor evaporator coils of mini-split A/C units?


  61. Lyndhurst Bodden August 11, 2016 at 12:52 pm - Reply

    Can I use H7 cleaner to clean/wash my condenser unit coils?

    • Bob Jackson August 12, 2016 at 4:11 pm - Reply

      I can’t say because I’m unable to find usage instructions, USDA authorization or Material Safety Data Sheet (MSDS) for H7 Industrial Cleaner and Degreaser on the Huerta Chemical Corp website. It’s unknown to me if H7 is a “no rinse” cleaner or safe for indoor evaporator cleaning.

  62. Dave orman May 31, 2017 at 10:59 pm - Reply

    I can flush my lines as this last time they were full of white junk and nasty. Problem I have is there is no drop . It’s almost 30 feet to outside the house. I need to find a vent or something closer don’t i?
    It’s easy to get to I use a ladder.i want caution everyone in an attic…be careful! Our ceiling joists are on 2 foot centers. The board under the front was 1/4 plywood. I fell and landed on my side. I did ok. I have 30 years as a firefighter and have went through a dozen ceilings but on 16 inch centers and my airpack catches and I swing back up. Never just fell through to ground. I have fallen through 2 roofs. Long story not good outcome on one buy this is related to ceilings.
    Back to question! Is 30 to long and can I run drain to plumbing vents? Out through soffit?

    • Bob Jackson June 1, 2017 at 8:23 am - Reply

      The evaporator coil condensate drain line is clogging due to insufficient slope and it’s a 30 feet run from the air attic handler to soffit, correct? Is your air handler a horizontal unit that lays on it’s side such that the condensate drain pan outlet is low above the joists? For comparison my attic air handler is an upright unit and the condensate drain outlet is a couple of feet high above the joists.

      The slope or drop should be at least 1/4 inch per foot for pipes 2-1/2 inches or less in diameter for gravity drainage. A 30 feet long horizontal run of pipe would have to be 7.5 feet high at the air handler to maintain a 1/4 in per ft slope which is way higher than any air handler/evaporator coil case.

      A better solution is to install a condensate drain pump by the air handler to pump the water out the drain line to the soffit. After that gravity will do the rest taking it down the exterior drain line to ground level. Set the pump in the auxiliary drain pan with the air handler as extra safety measure. The pump has an overflow safety shutoff switch that must be wired to the air handler to turn Off the A/C if the pump fails to prevent flooding.

  63. David S. July 6, 2017 at 5:36 am - Reply

    After our central a/c system has been on for a while, a mild but annoying odor of burnt paper permeates the house, like the smell of a cigarette that’s burnt down to its filter. I changed our filters today, smell still there. Any suggestions please?

    • Bob Jackson July 6, 2017 at 8:48 am - Reply

      Something in the air handler is over heating. Could be a wire, capacitor, blower motor or maybe a chunk of insulation has worked loose and blocking the air flow. Have it checked by an HVAC service company right away.

  64. Alan July 16, 2017 at 2:45 am - Reply

    Is my system finished?someone brushed all the evaporator blades together, I mean they look like a matted mess of metal. Is there any way to get the air flow somewhat normal? Drill holes, straighten blades, anyway to increase air flow? I think it’s a goner. Still works but flow is decreased by half.

  65. Eddy July 18, 2017 at 8:41 pm - Reply

    Hey Bob,

    I wanted to personally thank you for this “How-To”. We’ve been sweltering in the heat with inefficient AC and I didn’t want my landlord to pay for an expense HVAC fix. I troubleshot everything I could (thermostat, breakers, outdoor unit, filter) but it wasn’t until your guide that I overcame my hesitancy to actually open up the unit.

    I took off the condenser coil cover and WOAH! It was Christmas in July on those condenser coils with a huge block of ice occupying almost the entire housing! I’m currently defrosting the system with a new filter in place (we just moved in and the last filter was absolutely disgusting) and I’m hoping it’ll pump out cold air once it’s fully defrosted.

    Next question: if it refreezes after we thaw it, does that point us to determining the unit is low on a refrigerant?

    Thanks again for the help!

    • Bob Jackson July 19, 2017 at 11:37 am - Reply

      Unless your lease/rental agreement says otherwise, the landlord is responsible for property maintenance. The fact that the air filter was “absolutely disgusting” indicates routine maintenance isn’t being done. The landlord should have at least checked the air filter after the last tenant moved out. A clogged air filter can cause the coils to ice over by restricting the air flow but if it happens again soon it’s strong indicator the refrigerant charge is low and/or there’s a leak. If so, it will require servicing by an HVAC professional.

  66. Michele November 4, 2017 at 11:21 am - Reply


    My home is a tri-level and is 30 years old and we just replaced the 2 furnace units. We have a furnace that services the main floor and one that services the basement and upstairs bedrooms. The furnace that services the main floor has ductwork that flows through the crawl space. We sometimes get a really musty smell coming from the vents on our main floor and we cannot determine the source of the smell. We have had the ductwork sealed in the crawl space, and the smell that we’re getting is completely different than the “crawl space” smell. I am learning more about the evaporator coil, which is still the original, and I’m wondering if that could be the source of the musty water smell? we do not see any evidence of water leakage from the evaporator pan, but when the main floor furnace was replaced, it was completely rusted out. Can you suggest where our problem might be coming from? Does it make sense to think it could be old water from the evaporator coil? We are having the duct work and coil cleaned today, but I wondered if there is something I might be missing?

    • michele November 4, 2017 at 11:25 am - Reply


      also, our crawl space is encapsulated and we’re going to replace the humidifiers.

      • Bob Jackson November 4, 2017 at 2:35 pm - Reply

        You “just replaced the 2 furnace units” only as clarified in your comment “I am learning more about the evaporator coil, which is still the original“. My bet is the odor is caused by mold/mildew on the evaporator coil. If it’s matted with dirt and mold, check the air filter slot and return plenum for leaks as anything that gets past the filter will get caught on the coils.

        Ask the HVAC tech to also clean inside the evaporator coil because this is the “upwind” side where dust/dirt gets blown against and sticks to the fins.

        Consider installing an Ultraviolet lamp to inhibit mildew and algae growth. Also drop in a couple of drain pan disinfectant tablets every month or two during the summer. It will keep the drain pan clean and help keep the condensate drain line from clogging.

        The outdoor compressor on my 17 year old central AC system was failing this summer. I had it replaced with a high efficiency Bryant Evolution system. I was careful to ensure the evaporator coil end plate was removable should the inside ever need cleaning. I plan to install a UV light system on it before Spring.

  67. Scott December 23, 2017 at 4:49 pm - Reply

    Hello Bob. I have a Trane heat pump and Lenox furnace. Robertshaw 9420 thermostat. Backup heat is propane. Normal operation had been when heat pump can’t keep up, the heat pump and furnace blower turn off. Then the propane heat starts. Then roughly 20 seconds once propane starts up the furnace blower comes back on to move the air. It is usually very warm air coming out the vents right away after blower goes on.
    This winter I’ve noticed a concern several times when it tries to switch over to propane. The blower does not go off during the changeover. As a result it seems like warm air is not being moved after the propane runs awhile. Could this be a thermostat issue that’s not controlling the furnace blower correctly during the changeover process? It does not do it every time, of course. Thanks.

    • Bob Jackson December 23, 2017 at 6:14 pm - Reply

      Have an HVAC professional run a diagnostic on your hybrid fuel (electric/propane) system. It could be the thermostat, outdoor temperature sensor, control board or other problem. Then you’ll know if it’s something simple or a replacement part is needed.

      • Scott December 23, 2017 at 8:18 pm - Reply

        Thanks Bob. I appreciate your time and advice

  68. Rhiannon February 21, 2018 at 9:28 pm - Reply

    Hi Bob! Great article, very helpful. When I started reading the replies I thought there was no way that you would still be answering questions so many years later.. but you are!

    So our air is running and blowing cold air out or all the vents. Seems normal. But it has started freezing up. I know it coolant level shouldn’t be the problem since it’s blowing cold air. The filter is brand new and not dirty at all. Checked the coils certain that would be the issue and was shocked they were spotless. What else could it be?! The unit is not old at all. Maybe 3-5 years. We have VERY bad luck with HVAC repair men!

    Thanks again

    • Bob Jackson February 22, 2018 at 8:51 am - Reply

      The most likely cause is the refrigerant charge is low. It’s leaked over the winter and you’re noticing the problem now with the unusually warm weather this February. A leak test will cost around $300. Also check your warranty papers to see if your system is covered.

      AC evaporator coils are a heat exchanger. High pressure liquid refrigerant from the outdoor condenser (compressor unit) enters the evaporator coils and is flashed to a cold low pressure gas through an expansion valve. Expanding gas has a lower pressure and temperature. To use a crude analogy, it’s how freeze away wart remover works.

      If the refrigerant charge is low the gas pressure in the coils will be lower than normal, and therefore the temperature. When the gas temperature drops below the freezing point of water, condensation freezes on the coils. It’s a vicious cycle because frozen water blocks the air flow which would warm the coils, the coils get colder and colder causing more ice to form over a larger area. In really bad situations the coils can become a block of ice.

      • Rhiannon June 13, 2018 at 11:08 am - Reply

        Hi again Bob!

        Just now getting around to having a repair person out after a spring with lots of unexpected expenses. They looked at our unit and said that there is a leak in coils. They said the entire unit needs replacing and that the outside unit would also have to be replaced because they would not be compatible. The main unit is about 5 years old and the outside unit is about 3. They quoted almost 9 thousand. That seems ridiculous to me. Can a leak not be fixed? They said that the main system should be under a 10 year warranty but whoever installed it must not have turned in the paperwork so the warranty has expired. Of course we wanted a second opinion because that is not doable for us, but I wanted to get your thoughts.

        • Bob Jackson June 13, 2018 at 8:40 pm - Reply

          Contact the manufacturer to see if they have a warranty registration record. Have the air handler, coil and outdoor condenser serial numbers ready.

          > They looked at our unit and said that there is a leak in coils.
          Did the technician do a leak test? There are several types of leak tests, including: handheld electronic detector, bubble solution, fluorescent dye and nitrogen. A leak test can isolate the leak source(s) as it could be a failed brazed joint (relatively low cost fix) or many leaks in a corroded evaporator coil (expensive as replacement is normally required).

          * Bubble testing is spraying a soapy solution on the tubes and looking for bubbles.
          * Fluorescent dye is especially good at finding slow/small leaks and leaks within the coils. Dye is injected into the system which mixes with the refrigerant.
          * Nitrogen testing is more expensive because the refrigerant is removed, then the system is charged with nitrogen. The gauges are checked for pressure drop and leaks may be heard by ear or ultrasonic detector. Bubble testing suspected leaks can confirm the exact location.

          HVAC techs I’ve spoken with prefer the bubble and dye test for visual confirmation and inspecting those hard to reach places. This test runs about $300.

          Outdoor condenser coil leaks can be repaired more easily than evaporator coils because the condenser is easier to access. My nephew once shot a blowgun dart into my brother’s condenser coil. The tech repaired the hole for several hundred dollars. That was the end of the blowgun!

          Back to your 3 year old air handler/evaporator coils with a 5 year old condenser; do the leak test first to isolate the problem… poor workmanship (e.g. leaking brazed joint) vs a problem with indoor or outdoor coils. I believe an early life problem like yours is caused by poor workmanship. e.g. Fix the leaking joint(s) by evacuating the refrigerant, redoing the joint(s) and recharge the system.

          Coils can be replaced if the leak is within the evaporator coils. That may cost $600 to $1200 depending on the make/model. Shop around for quotes because compatible replacement coils should be available for major brands.

          Should you decide to buy a new system, this article may be informative: Old Central Air Conditioning Replacement with New Bryant Evolution High Efficiency System. I spend ~$8,400 on the first and $8,600 on the 2nd central AC unit.

          Let me know what happens.

  69. Marilyn Mack April 1, 2018 at 4:52 pm - Reply

    Help! My coils and fan have mold. How does one know if the coil and fan have to be replaced or cleaning them will work? Have pics I can share. In Florida and need done before having to turn on the AC.

    Shouldn’t this have been checked with pricey home inspection?

    • Bob Jackson April 2, 2018 at 7:30 am - Reply

      The decision to replace or clean the AC evaporator coils depends on several factors.
      * How old is the AC system? If over 10 years old it may not be worth repairing.
      * Are the other problems with the system? Is it leaking refrigerant? Is the outdoor condenser unit in good working order?
      * Can the evaporator coils be successfully cleaned?
      * When was the last time the system was serviced?

      It’s apparent the former homeowner neglected the system so there may be several maintenance issues.

      > Shouldn’t this have been checked with pricey home inspection?
      A home inspector will only perform cursory heating & air system checks. If the inspector was recommended by the realtor they tend to minimize problems to facilitate the sale because the inspector is dependent upon future referrals from the realtor. Best to hire an inspector own your own, then hire a licensed HVAC company to thoroughly inspect the AC system, including opening up the air handler to inspect the coils.

      At this point, you should hire an HVAC company to do a complete health check. Cleaning the coils will help but won’t make much difference if the refrigerant charge is low, the coils are leaking or the compressor is going bad.

      For cleaning very dirty coils see:
      Heavy Duty AC Evaporator Coil Cleaning
      How to Clean Inside of AC Evaporator Coils

  70. JJ May 17, 2018 at 11:39 pm - Reply

    Hi Bob. I have an all-electric house with the air handler blower located in my attic. Just turned on the air conditioner yesterday and came home from lunch today and noticed it wasn’t as cool as I would have expected. Went to the outside unit and noticed that it was freezing up outside. At that point I turned the AC off but kept the blower running as I had a service guy out in August of last year and that’s what he told me to do prior to him coming. He said I was low on Freon and added some to it and it worked fine the rest of the season. After about an hour and a half or two of just the blower running it was unfrozen so I turn the unit back on and went to work and return home to find the house nice and cool. Right before bed though my wife came in from outside to tell me that there was water pouring out of a vent located under the soffit of the roof. I’m just wondering if you’ve ever seen a backup to the primary condensation ran to an outside vent like that. I also noticed it freezing up again outside so I turn the AC off and we’ll let the blower run the rest of the night as I have a repair guy coming out tomorrow to take a look at it. The unit is approximately 15 to 16 years old just wondering what your thoughts are. Thanks from Mr. Unhandy!

    • Bob Jackson May 18, 2018 at 8:22 am - Reply

      The HVAC tech will surely find your AC system has a leak and is low on refrigerant. See the “Evaporator Coil Icing & Freezing” section in How to Clean AC Evaporator Coils – Part 2 about low refrigerant charge and the Joule Thomson Effect.

      > Went to the outside unit and noticed that it was freezing up outside.
      The air handler evaporator coils are freezing to such a degree that the return line to the outdoor condenser is below 32 degrees F, causing it to ice up too.

      > my wife came in from outside to tell me that there was
      > water pouring out of a vent located under the soffit of the roof.
      It’s common for the 3/4 inch secondary drain pan line to be poking down a few inches from the soffit. If the contractor was lazy they may have just set the pipe on a soffit vent. When the block of ice on the evaporator coils started to thaw, the coil condensate drain line was frozen causing the water to overflow and run down the air handler into the secondary drain pan, then out that drain line to soffit.

      > The unit is approximately 15 to 16 years old just wondering
      > what your thoughts are.
      The old system at or near the end of it’s useful operating life where you’ll have to decide if it’s worth repairing such an old system. I replaced my old units with a Bryant Evolution system.

  71. brad v June 3, 2018 at 10:02 pm - Reply

    Hi, Thanks for the write up!

    So i have a FirstCo – 1 1/2 Ton Horizontal Ceiling Mount 240V Motor.. i took the duct vent cover off to clean the “out” side of the Evaporator Coils. But can’t seem to find a way to get in past the blower motor/fans.. i can see through the fan blades and looks like an 1/8″ of dust on the coils.

    Any info on how to get access to a unit like this would be appreciated!

    thank you!

    • Bob Jackson June 4, 2018 at 8:36 am - Reply

      I’m guessing your First Company Products (FirstCo) fan coil is similar to the HX(-C) Series. If you look at the diagram in the previous link, the blower assembly is likely a bolt-on unit.

      To access the back or upwind side of the coils closest to the blower motor, shutoff the circuit breaker, disconnect the blower motor electrical cable (power feed) and unbolt the blower assembly. The next question is does your unit have a heater coil in front of the evaporator coil? The heater coil may need cleaning and it will limit access to the evaporator coils.

      The Mini-Split Bib® Kit is designed for cleaning fan coils. It’s available at The idea spraying the cleaner through the coils should wash dirt off the back of the coils. Also see AC Evaporator Coil Cleaning with Pump Sprayer and Brush.

      • Steven T December 16, 2018 at 8:12 am - Reply

        Bob Jackson, I don’t know who you are. You seem to be a very great person. I’ve read most of these comments on this page. I’ve never seen someone as caring as you. People aren’t nice anymore, they’re just lazy or plain evil. You are rare.

        I’m writing this because I am poor, due to a number of circumstances much like many others out there. I am however fortunate enough to have a roof over my head, even if it’s not the best. Anyway… the point. I live in a Condo near Chicago (cold), my furnace + ac was replaced about 5 years ago. Furnace has been broken since last year. When I say broken, it’s more my term. I called HVAC company that installed it, charged me didn’t help (worked for 4 days). Went to another place, they charged me a lot for an emergency call (wrote on sheet adjusted blower speed) stopped working again in few days. Came out again (same place as 2nd time) charged me again didn’t fix it. Finally I complain on Yelp, ‘boss’ comes out got it working for free (probably mid Jan) didn’t tell me the problem or what he did to fix it. Now it’s broken again, same problem. I thought it was dirty flame sensor so I bought & replaced it myself didn’t fix it. Blower turns on (crappy 1 stage furnace), igniter turns on, gas comes out about 40 seconds later & usually lights. It’ll run for few minutes, turns off? Try to start to again, does same thing or gas won’t even light? I don’t know. What is wrong with it? I can’t afford to call people, & even if I did I feel they won’t help. How can I ensure a service call will fix the issue? Can I refuse to pay till it works for a week? What are my options?

        Now looking at this, I’m not very smart. I was really confused before about what that box on top of the furnace was. Your picture helped a lot. I have same thing, upflow setup with ac box on top. Now when reading this I got confused again. The AC affects the furnace? If the AC coil is dirty will the furnace not work? Could taking off the front & using that spray cleaner fix my furnace problem? I’m really desperate, I’m sorry this is so long. If you read it and respond. You truly are a great person. I’m crying right now just thinking about how you might help me.

        • Bob Jackson December 16, 2018 at 1:46 pm - Reply

          Hi Steven,
          To summarize the problem with your gas furnace:
          * 5 year old central heat and air system.
          * Furnace runs for a while then shuts off.
          * Several service calls haven’t fixed the problem.
          * Service tech adjusted blower motor speed.
          * You’ve replaced flame sensor.

          Is the furnace out of warranty?

          When a HVAC service tech visits, be sure to ask for a detailed report itemizing what diagnostic steps were performed, problems found, adjustments made or parts replaced. Review the report with the service tech so you understand what was done. Make your own notes in laymen’s terms if needed because the service report / invoice can be a bit brief. The next time a service tech comes out, have the prior service reports available.

          Adjusting the blower motor speed – I assume the speed was increased for greater airflow – suggests insufficient airflow, which can cause the heat exchanger to overheat and trip a limit thermostat. This can be caused by a dirty air filter, dirty blower wheel or a clogged evaporator coil. Do you feel a strong airflow from the ceiling and floor vents when the furnace is running? Are the vents fully open?

          Air flow problems:
          Replace the air filter monthly. The service tech would have already noted a dirty blower wheel, so I think that isn’t the problem. To check the evaporator coil, inspect the coils as explained in these projects:

          * Heavy Duty AC Evaporator Coil Cleaning
          If you can shine a flashlight through the coils, then they’re clean inside & out and no further action is needed.

          * How to Clean Inside of AC Evaporator Coils
          The interior coil faces may be clogged if you cannot shine a flashlight through the coils.

          Probable Reasons Why Your Furnace Runs Only For a Few Minutes discusses other possibilities.

          The pressure switch could be shutting off the furnace. Gas furnace pressure switch problems explains it’s often not a faulty pressure, but a defective inducer motor (it’s the small motor on the front of the furnace).

          Let me know what ultimately the fixes the problem.

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