Air Conditioning Cleaning: How To Clean Central A/C Evaporator Coils

This article is a compliment to “How To Clean Central A/C  Condenser Unit Coils”. For the purpose of this article, we’ll be discussing air conditioner evaporator coil cleaning inside of the air handler of a split central air system, typical of air conditioning systems in the Dallas area. My central air conditioning system happens to contain a natural gas furnace for heating.

Your air handler is composed of a blower motor, the furnace, and the evaporator coils. You can easily see which compartment your evaporator coils are located inside of by looking for the refrigerant lines and where they come out of the air handler. There are 2 refrigerant lines. One is larger and one is smaller. The larger one is low pressure and contains freon in it’s gas form. It will feel cold when your air conditioner is running. The smaller one is a high pressure, high temperature line that contains refrigerant in it’s liquid form.

air conditioner evaporator coil cleaning attic diagram

Here is the air handler in my attic. You can see that it is hung from the ceiling and happens to be missing a secondary drain pan. Something I need to address. Because of the low overhead I had to shoot this picture from one side.

As air is blown across the evaporator coils, the air around it cools and blows that cooled air into your home through the duct work. When the evaporator coils begin to become coated with dirt, dust and grime, they don’t cool the air flowing over them efficiently, causing your system to work more to cool your home.

attic air handler image with descriptives

The above photo is from the other side, which clearly shows the evaporator coil compartment. There was a lot of foil tape around it from the last person who did a maintenance.

Air Conditioner Evaporator Coil Cleaning Tools You’ll Need:

1. No-rinse spray on foaming cleaner for coils
2. A few basic tools
3. Roll of foil tape
4. Bleach/water mixture in a garden sprayer
5. Portable vacuum or shop vac

Here’s what to do:

First, turn the thermostat to the off position. You can also flip the switch located near your furnace to shut off power to your unit.You’ll need to locate the evaporator coils within your air handler. This will be the section where the freon lines enter. There is a sheet metal panel attached to the air handler which will need to be removed. It’s attached by sheet metal screws, and the edges are usually taped with foil tape to prevent too much cold air from escaping. Be careful not to damage your freon lines as you remove the panel.

air conditioner evaporator coil cleaning remove the aluminum panel

There were 13 screws all together to remove the side panel as well as open the top panel of the evaporator compartment of this unit. I had to open the top to access all of the coils. The side panel on this unit had to be rotated after removing the screws to clear the freon lines.

Your evaporator coils should be visible and you should have enough room to clean the coils. If your unit does not allow enough room to comfortably work, I recommend hiring a pro. At the least, you can visually inspect your coils once the panel is removed.

evaporator coils in compartment

This photo was taken after spraying and rinsing the coils, but shows how your evaporator coils look within the compartment. You can see foam from the foaming spray cleaner floating in the bottom drain pan. This evaporator is original equipment in this house, which was built in 1994. Not too bad considering that it is highly unlikely that anyone has cleaned the coils in several years.

Begin by spray a foaming cleaner on both sides of the coils to loosen the dirt and grime. You can get a no-rinse foaming coil cleaner which will do the job just fine. I used WEB WCOIL Coil Cleaner on this unit. An evaporator can remove many gallons of water from the air inside your home in a day! The condensation will more than rinse the coils. I always spray the coils with a mixture of bleach and water using a garden sprayer to help inhibit mold growth. About 1 cup of bleach to a gallon of water works very well. Never use acid based chemicals to clean your coils!

(Even though vinegar is acidic, you could use it as an alternative, but the smell isn’t very pleasant. Either way, clean your coils on a warm day so the condensate will help rinse everything.)

air conditioner evaporator coil cleaning spray

You can see the dust and dirt build-up on the inside of the coils (above). After spraying and carefully brushing the coils, I sprayed everything with a bleach/water mixture.


I used this garden sprayer filled with water and 1 cup of beach to spray the coils after the foaming cleaner. I very carefully brushed all 4 sides of the evaporator coils with the brush shown, although a toilet bowl brush works very well too. Remember to be very, very careful when brushing the delicate fins of your evaporator coil.

Then, I pour the remaining bleach/water mixture I have left in my garden sprayer into the drain lines to keep them free of algae buildup. A clogged drain line can cause your drain pan to overflow and cause extensive ceiling water damage. I used the remaining bleach/water mixture from my garden sprayer and poured it directly into the drain pan. The house will have a very mild bleach aroma for about a day. Unless you are sensitive to it, there is no real concern, it is a very mild smell that dissipates quickly.

When you are done, replace the panel, screws and use foil tape to seal the edges of the panel.

Panel replaced, edges taped and I felt along all sides to be sure I did not feel any cold drafts!

Your Dallas Handyman Top 5 Tips:
1. When your air handler is open you can look inside and do a visual inspection of the amount of rust, grime and mold accumulated on the evaporator coils. Also check the pan for rust and holes. Perhaps the best pan to have is a plastic drain pan, which are available. Hire a pro to replace the pan or coils when needed. There should also be a secondary pan under the air handler equipped with a cutoff switch in case the evaporator drain pan fails.

2. Air conditioner evaporator coil cleaning should be performed twice yearly. Once in the spring before the cooling season and once in the fall before the heating season. Good maintenance will save you money every month on your utility bill and keep you from replacing major parts on your system prematurely. Heating and cooling your home is the single highest expense most homeowners have on a month-to-month basis.

3. Air conditioner evaporator coil cleaning is not a difficult job! Take your time and do a good job and expect to spend an hour or more your first time through. As you gain confidence and experience you’ll get faster. And you’ll always know how the internal parts of your air conditioner are doing.

4. Hire an HVAC (Heating, Ventilation and Air Conditioning) contractor to inspect your entire system before buying your next house; you will know what to expect out of your heating and cooling system going into your new home. They can usually tell you how old your heating and cooling systems are, and how much life is left in them.

Most home inspectors check the operation of your heating and air conditioning system but many do not open air handlers or report their true condition. The cost of an HVAC specific inspection could save you thousands of dollars alone. Air conditioner problems are rarely inexpensive to fix.

5. Clean and inspect: While your panel is off to the evaporator, use a Good Quality Shop Vac for some of the areas to vacuum out dust. Extensions can help you get pretty far into the duct work, and it can make a huge difference.

Look for rust and leaks on the drain pan. A failed drain pan can possibly cause your system to shut down and may cause extensive ceiling damage. Be sure you change your system filter every thirty days. It’s located in your air handler in front of your blower or behind the return vent inside your home. You can hire a handyman to clean your coils for you for less than a full service call from an A/C pro, but a handyman cannot check freon levels or add freon.

So there you go. Feel free to send in your comments, click a social button at the top of this post so your friends can check it out too, and good luck!

This Post Has 30 Comments

  1. This is a great article. Thank you so much for sharing!
    My house was built in 1994. My HVAC has the same air handler as the one you described. I live in Phoenix area so the AC is very important to us in the summer. Luckily, my system never had any problem and it still works efficiently. Regardless, I always felt that I should clean the evaporator coil or at least I’d like to check to see how dirty it is. However I never did since I did not know where to start. You article described it very clear and made me feel confident that I even could do it myself. Thanks again for sharing!

  2. Hey Chuck,
    If you’ve never looked inside your air handler, you may be in for a surprise. The air handler in the pics was installed in 1994 as well, and even though it was fairly clean, I was able to rid the coils of a lot of dust and dirt. This one had earmarks of having been maintained maybe 4 or 5 years ago (newer foil tape around the coil compartment). Keep those filters changed! Good luck and thanks for commenting! – Phil

  3. Hi, thanks a lot for an excellent article. I do have a bit different situation, and would like your advice. I live in Panama City, Panama and the humidity is horrible all year round due to what is like an island (a small country) surrounded by oceans. I have a 24,000 BTU Sankey split on the wall unit. A man so-called cleaned the unit 3 months ago because we are getting water in our house from the evaporator unit. He hosed down the coils with a garden hose (small concentrated spray of water) with a big plastic sheet below to catch any water that fell towards the tile floor. However, now in 3 months we are having water come into the house again due to an obvious drain line plugged. I have read the owners manual and it does not show the pan location nor how to clean the unit. I have looked on the internet but can not seem to find a Sankey home page for help. Can you please help by telling me how to unplug the drain pan inside the house, and where is the drain pan located, and also does the unit (evaporator side) in the house have to be removed? Many questions and looking forward to any help I can get. Thank you in advance. Mike in Panama

  4. Hi Mike.

    I couldn’t find repair manuals either for your unit. I can tell you a couple of things, though. Almost invariably, dripping from the front of the unit is caused by the incorrect slope of the unit. If the drain is slightly clogged and the slope is inadequate, you’ll probably get water accumulation. Too much accumulation and you’ll get a flood. The front panel can come off usually by removing a couple of screws and lifting the panel up and away. You may have to remove the unit from the wall but probably not. Inside you can clean the evaporator coils and see the drain pan at the bottom of the unit. Not knowing what kind of drain you have (is it a hose or a hole on the outside?) it’s hard to say exactly what may be slowing the drain down. A good tool to have for clearing freezer drain lines (for example) is a narrow cable like what’s used on the brakes of a bicycle. You can run that flex cable through your drain to clear it out. If you see a foam air filter with the unit apart, check it to be sure it’s in good shape or if it’s dirty. Either way, clean it or replace it. Hope this helped…sight unseen 🙂

  5. Thank you very much, Phil. Haven’t had time to check out location of the screws you mentioned just yet, but will. To answer one question you asked is that the drain line goes through a hole to an outside wall and into a p.v.c pipe to a drain canal alongside my house.
    The exterior side hose leaving the house is a spiral ribbed type hose that came with the unit and was installed by the company that sold the unit. We didn’t have any problems with water coming inside for 2 years and now we’re going on the third year and it is starting to drain water inside the house. Last weekend, using your guide on cleaning (1 cup of bleach to 1 gallon of water) I first vacuumed the unit, used a toothbrush to clean the rotor fan blades (very dirty) and then sprayed with your suggested chorine mix. The unit has been running for 3 days and so far no water in the house. It also seems colder. The rotary fan blades were at least blocked by 50 percent and now maybe 10 percent after extensive cleaning. I will go clean some more in two weeks. Thanks very much for your help and also answering my e-mail message. You have been super helpful. Mike in Panama, Panama.

  6. Nice article! My house was built in 1980. New air conditioning units were installed in 96. They’ve never been cleaned since then. I think I could clean the outdoor units; no prob. with these instructions. BUT for part 2, it’s in the attic? Where the bugs & other creatures may be lurking? I have my coveralls but don’t think that’s enough protection. Any suggestions? I can’t afford to hire anyone & this must to be my project….

  7. Hi Coleen, Thanks for the interesting question…I really don’t think you will have too many issues with bugs since there’s nothing for them to eat in the attic. The worst issues you’ll face are accessibility to your evaporator coils and insulation dust. A long-sleeved shirt is a great thing when working in the attic and be sure to wear a breathing mask. A cheap one from the hardware store should be sufficient. That should be all the protection you need. You might want to be wary of a possible bee hive though. Let me know how it works out! Phil

  8. Hi Phil, I read your article about how to clean an attic AC unit coils… My concern is how to even open up the unit… I have a furnace on one side, then the ac unit and then an insulated square “box” on the other side. I can figure out that the clean sheet metal unit is the ac, but I dont see many screws or panels to access this unit…? The ac unit is about 11 years old and just last night it stopped blowing cold air, the compressor outside was spinning but no cold air from the vents inside the house. I climbed up into the attic to see lots of water coming out from under this unit into the drip pan, and some water dripping out from under the insulated “square box” on the end of the unit? The copper pipe that is insulated was nearly frozen (ice build up under the pipe once I pulled back the rubber insulation….? I turned off the ac and ran the heat (it was 84 already in the house) but this seemed to work since lots more water started to drip.
    What caused this and how to fix it?
    Should I try to open this attic unit and clean the coils?
    How do I oil the fan motor and where is it?
    Thank you and great article

    > Dave

  9. Hi Dave,

    Thanks for posting. First you are on the right track to clean the coils. So, yes, you should open it up and clean it. Feeze-ups are caused by inadequate air flow across the coils (which can be caused by a few different things, dirty coils being a primary one). It sounds like you may also have a partially clogged drain line if there is a lot of water in other places than at the drip pan.

    You don’t need to run the heat to thaw it out, but it’s a good idea to run the unit in “fan” mode while it thaws although you can just turn it off.

    My suggestion is to clean the evaporator coils and compartment first. Then make sure you have a clear drain line.If you have an air compressor you can “blow out” the drain line pretty easily. Some bleach poured directly into the line will kill any algae built up in there too. Then go outside and clean the compressor coils as well. (I have an article on that too if you need to check it out) Finally change out the filter.

    Once everything is clean and back together, turn your unit back on and see if it freezes again. If it does, you are probably low on freon. Call someone to check/charge your system. There are a couple more possible issues, but a good cleaning will get you on track to a good repair if it doesn’t solve it altogether.

    I hope this helps. Don’t be afraid to get that compartment open! Once you are “inside”, your halfway done.

    The blower motor is located before the evaporator coil, and just before the furnace. It is first in line. Expose the blower motor and spin it by hand. It should spin easily and freely. There should be a couple of ports near the shaft (if it is NOT oil-less). put a couple of drops of 3-in-1 oil into the ports and spin the motor again. If the motor does not spin freely after oiling, replace it.

    I hope this helps and good luck!

  10. Howdy, I do think your site may be having internet browser compatibility problems.
    When I take a look at your blog in Safari,
    it looks fine however, if opening in I.E.
    , it has some overlapping issues. I merely wanted to
    provide you with a quick heads up! Aside from
    that, excellent blog!

  11. Hi,
    I live in a trailer and the ac unit is located in a small closet with access only from the front of the closet. The space surrounding the unit is not large enough to see or get behind. Recently the coils on the unit have ice build up. Any suggestions on how i can get in and take a look at the unit?

  12. Hi, Thanks for the photos — they really explain it well! I have a Goodman air handler/gas furnace in my Phoenix attic, and I need to clean the coils, but I was told this type of unit can’t be opened in a way that provides access to the dirty side of the coils, and that I would need to evacuate the refrigerant and have the coils cut out to be cleaned. Do you know a workaround for this? thanks a lot!

  13. Hey Billy,

    I always want to know when there are browser compatibility problems with the site. In 2013, the plan is to have a completely responsive site for all users. In the meantime, I have updated the site for newer browsers and it should be better. I’ve checked it with Firefox, Chrome and Safari on both Mac and PC. Hope it did some good~! UPDATE! (April, 2014) – Your Dallas Handyman is now responsive. It looks great on my Android! 😉

  14. Hi Phil,

    Great article. I wish I had seen it before my husband did the following 24 hours ago to our AC evaporator coil. Here is what my husband did. He blocked up the drain line going to the sump pump. He poured bleach into the coil pan (which emptied into the drain line). He filled until the pan was full. He let it sit for a period of time and then drained. He then flushed with water (2 of the blue buckets full – a little at a time to not overflow).

    11 hours after the cleaning, the AC went on with a new filter in there. The moldy fungal smell is gone, but has been replaced by an overpowering bleach smell. My concern is if it is safe to keep the AC on and how long will it be putting out that bleach smell? I am super sensitive to bleach smell. I am also concerned about the new filter we put in since it will now be bleachy. However, we need to keep it in there for allergy purposes to properly filter the air.



  15. Hi Sheila,

    Thanks for reading and thanks for your comments. The great news is that your A-coils are probably very clean now! 🙂 If you’re worried about the bleach odor, then you might want to wait to run your A/C until you leave the house, and you could just run the fan to help clear the odor a little faster or even open a few windows. But, the answer I think you’re really looking for is that the smell will begin to dissipate immediately and will be pretty much all gone in just a couple of days. Hope that helps. Phil

  16. Hi Phil,

    I recently found out we have mold build up on ouur coils, My ac coil unit is in an upstairs closet hanging over the hot water heater and it’s complicated to get too. My question is: Is it safe to use a bleach spray on the coils to clean it Since I can’t really get that far into the closet to reach it with the heater in the way or is it better to use a vingar solution to do such and will it harm the coils in any way? Thanks in advanced for the help.

  17. Hi Phil,

    I live in North Dallas. I have 2 a/c units where the metal drip pans have rusted out. On one, a handyman friend of mine unfastened it, turned it around, drilled a new hole in it and it drains fine now. On that same unit, he told me to take a dry/wet shop vac and suck out the gunk/rust debris that was clogging the main drain. There was no open trap on the drain, so I bought some PVC pipe, a T, connector and extra pipe and added a trap (?). I used the shop vac to unclog the main drain which it did. However, I then noticed that the dripping is coming from underneath the evaporator coil housing. Upon inspection of the other a/c unit evaporator coil and housing, I found the same problem only the housing rusting is a bit worse. What is my best option given that both housings (is that what you call the metal box that holds the evaporator coil?) are rusted on the bottom near the drain? Should I have a new box created? Should I replace the evaporator coils on both? Thanks, Dave

  18. Hi Jewel. Neither vinegar nor bleach will harm your coils if you use them properly and rinse well. A couple of quick tricks: always use a 50/50 mixture. For mold I might recommend bleach to kill it. Clean your A-coils on a warm day so that the condensate will help rinse your coils after you are done. In this article I talk about a bleach and water mixture because I (personally) like the fresher smell over vinegar. It’s strong at first, but dissipates in less than a day and is unnoticeable after just a couple of days. If you prefer buying a foaming product, you can try a foaming cleaner designed for air conditioner coils.

  19. Thanks Phil, after reading this in my 30 year old home I opened up the unit, wow I was amazed at all the hair an dead skin collected over the years! Cleaned it all up even re-strung one of the heat coils, ty for posting this it was really easy to do. Now I will maintain it yearly, amazing how much better the house smells now too

  20. After searching the internet, I finally found your site. Thank goodness for clear and concise directions! The pictures are so helpful. The unit I’m having problems with is a central AC in a Fla rental unit. My tenant keeps the unit on ALL the time and it has algae growing up the coils. I’ve tried the foaming cleanser and that does squat. Other then using a toothpick to dig it out (my current method), what can I try?

  21. Hi Debbi, Thanks for the comment. If you have really bad algae and you have resorted to using a toothpick, then it may be time for the big guns…When you have your compartment open, use bleach to kill the algae first. spray it on and let it sit. Then get some rags and clean everything up as good as you can and get everything as dry as possible. Once your coils are pretty dry (along with the dead algae all stuck in there and everything) then use compressed air to blow out your coils. You should check out my review on the Porter Cable Portable Air Compressor I use for such an occasion you described. That’s a major pro tip, and you can clear out the most stubborn problems you’ll encounter. Work carefully, and once you’ve blown everything out, follow up immediately with foaming cleaner to clean up the residue. Your shop vac is for the surrounding area mess you’ll make. Let me know how it works out!

  22. Thank you for the good photos of your system.
    My YORK unit was installed in my attic also….in 1994. It has NEVER been serviced!
    Here is Why: A very sick individual put it there! lol My attic is only a series of 2×4 trusses.
    I have spent the last several nights installing plywood boards from which I can access the hvac unit for servicing. My shins look like I have been playing Rugby with Cactus plants! I am just about worn out! 71 years old is too old for this! lol
    Wish me luck !

  23. Hi, I noticed my A/C lagging behind and called a technician to take a look at it. The evaporator coils are pretty dirty (on the outside, he didn’t look at the inside ?) He said normally he would take the coils out and give them a good cleaning with an acid solution, but because there is a small amount of rust at the bottom of the metal plate on the front, he was afraid it would leak after he put the coils back in. He recommended replacing the coils. The A/C was installed 4 years ago. The rust that is visible is minimal compared to some photos I have seen in DIY videos and pictures the internet, on coils that are still being used. Is it possible that a small amount of rust on a 4 year old coil would require replacement? It just isn’t sitting right with me….. but I know ZERO about HVAC.


  24. Hey Teddi…It would not be right for me to really comment either way about this unless I saw your condenser unit firsthand. However, I will offer one small suggestion: before you follow someone’s advice that might not sound right, you might want to follow your gut instinct first. Hire someone else and get a second opinion. Don’t say anything about the first guy. Just start over with someone else and see what they say. Make sure they are reputable.

  25. I am in Chicago and have a central ac unit under my deck outside my home. I took advantage of a program through our electric company to save money, instead our ac unit has been acting up since. The line going from the furnace to the outside unit keeps freezing and once this happens we turn the unit off and let it thaw out and turn it back on and it will work for about a day or so. We usually rinse the outside unit with the hose and give it a good cleaning and start it again and it gives us cool air in the house. We had an AC guy who said the unit is fine on the outside and to make sure we set the thermostat at the right temperature. Could the coils on the unit and in the furnace being causing these issues? Maybe bad air flow?

  26. It’s interesting that it started acting up right after you allowed your electric company to work on it. I really can’t comment on what’s actually happening, although I would consider hiring someone who can troubleshoot and find the cause. Setting the thermostat at any temperature is not a reason for freeze-ups. It could be low refrigerant or bad refrigerant or an airflow problem. You might try cleaning the A-coil in the furnace unit and make sure your fan is working properly. After that, I would suggest hiring a pro to look deeper into it.

  27. Hi! Honestly, I’ve been cleaning my a/c myself for about 5 or 6 years now. I live in the Savannah, GA area. First, I have to say that I have never heard of using bleach actually on the evaporator coils, and I was a bit concerned about that. Does the bleach do something more than the foaming coil cleaner? I usually use “EVAP FOAM NO RINSE” by Nu Calgon to clean the coils. My problem is my coil seems to get clogged a lot even with regular cleanings. My a/c guy recommended double filtering because of my cats, but this caused excessive mold and algae to build up on the coils. Do you have any suggestions? Also, as a person with a sensitivity to bleach, can you enlighten me on the purpose of the bleach when cleaning the coil? (I already pour bleach down the drain line every time I clean the unit — and I have to leave the house to give it time to dissipate.)

Leave a Reply

Your email address will not be published. Required fields are marked *