The A-frame evaporator coil front cover plate was removed to access the interior coils in How to Clean Inside of AC Evaporator Coils.

AC Evaporator Coil Inspection

The coils are 12+ years old and have never been cleaned from the inside. Overall the coils are not extremely dirty but do have some surprising mold, dust, dirt, insect bodies and debris. An important note is there is no evidence of oil on the copper coil circuits which would indicate a refrigerant leak (the HVAC service company checked my system last week and confirmed the refrigerant charge was fine). Note the air flows upward through the coils on my AC system so anything that gets past the air filter may stick to the coil faces:

AC Evaporator Coils Interior View before Cleaning

AC Evaporator Coils Interior View before Cleaning

Closeup of the right side of the coils. A fine layer of dust coats the fins with various clumps of dark stuff and what appears to be stringy pieces that may be a spider webs, pet hair or other fibers. That larger slightly silver colored object in the center turned out to be piece of HVAC metal foil tape:

Dirt and Dust Inside AC Evaporator Coils

Dirt and Dust Inside AC Evaporator Coils

View of the left side of the A-frame coils before cleaning. Note the dust line starts about 2 inches above the bottom of the coils (which are still shiny) because the plastic condensate drain pan blocks the air flow along the bottom section of the coils. The dust buildup is also greatest towards the back of the coils where the airflow is strongest directly above the blower housing outlet:

AC Evaporator Coil Cleaning - Interior Dirt

AC Evaporator Coil Cleaning – Interior Dirt

Looking down into the natural gas furnace and heat exchanger below the AC evaporator coils you can see how the drain pan (red arrow) shields the bottom of coils. The blower wheel is just visible at the yellow arrow:

AC Evaporator Coils and Gas Furnace Heat Exchanger

AC Evaporator Coils and Gas Furnace Heat Exchanger

I held the camera inside the A-frame coils to get this photo of the furnace heat exchanger, blower housing and blower wheel. The blower housing opening is located at the rear half of the furnace and begins at the two yellow lines. This is why the dirt buildup is worse towards the rear of the coils where the airflow is strongest:

Air Handler Gas Furnance Heat Exchanger and Blower Motor

Air Handler Gas Furnance Heat Exchanger and Blower Motor

My Heil natural gas furnace was made by International Comfort Products. This diagram from the Technical Support Manual illustrates the location of the blower outlet to better understand the layout:

Heil ICP Gas Furnace and Blower Motor

Heil ICP Gas Furnace and Blower Motor

AC Evaporator Coil Cleaning with Pump Sprayer and Brush

The HVAC techs clean evaporator coils with a professional grade alkaline cleaning solution and pump sprayer as explained in Heavy Duty AC Evaporator Coil Cleaning.

AC Evaporator Coil Cleaning with Nu Calgon Evap-Powr-C and Pump Sprayer

AC Evaporator Coil Cleaning with Nu Calgon Evap-Powr-C and Pump Sprayer

I’ll also use a 14 inch bench brush purchased at Home Depot that features “flagged poly fibers of this brush grab even the smallest dirt particles”. I chose this brush because the bristles are not so stiff that it will bend the coil fins if used correctly and the flagged poly fibers (i.e. really bad split ends) are like tiny fish hooks that does a great job picking off dirt. The long brush makes it easy to reach deep inside the coils. A fin straightening tool is handy for removing clumps that can’t be brushed off or fixing the fins if you accidentally dent them with the brush handle or your hand:

AC Evaporator Coil Cleaning: Bench Brush and Fin Straightening Tool

AC Evaporator Coil Cleaning: Bench Brush and Fin Straightening Tool

Spray and Clean the Evaporator Coils

The Nu-Calgon Evap-Powr-C solution is mixed and sprayed on the fins to loosen and remove the dirt. I noticed that even with a heavy thick stream the cleaning solution never shot through the coils, instead it wicked down the other side and into the condensate drain pan. Nice! But if you’re concerned about getting cleaning solution on the furnace heat exchanger or blower fan you can place towels over the heat exchanger. (Thanks to Scott A. for the towel tip!)

Cleaning AC Evaporator Coils with a Pump Sprayer

Cleaning AC Evaporator Coils with a Pump Sprayer

The large clumps of dirt/mold/whatever mostly came off with a concentrated spray. I often needed to direct the spray at a low angle across the coil face to peel off the clumps:

AC Evaporator Coil Interior Cleaning with Pump Sprayer

AC Evaporator Coil Interior Cleaning with Pump Sprayer

A sample of the debris I picked off the evaporator coils using only the pump sprayer. I think the stringy stuff is pet hair or lint. The dark globs are covered in mold. There’s even a moldy spider (gross!):

AC Evaporator Coil Cleaning - Dirt and Debris Removed from Coils

AC Evaporator Coil Cleaning – Dirt and Debris Removed from Coils

I used a full gallon of cleaning solution mixing 1 part Nu-Calgon Evap-Powr-C to 3 parts water, alternating between spraying both sides of the coils. I mixed another gallon of solution in the sprayer for the next steps to clean the coils with the bench brush.

A quick illustration of the fin straightening tool in case you need to comb out the fins. Choose the correct tool head size in threads-per-inch that match your fin spacing. I was careful and didn’t need the fin tool:

AC Evaporator Coil Cleaning - Fin Straightening Tool

AC Evaporator Coil Cleaning – Fin Straightening Tool

Cleaning Evaporator Coils with a Brush

The pump sprayer removed most of the dirt but “chunks” remained at the apex or narrow section near the top of the A-frame evaporator coils that were loose but I couldn’t wash off with the sprayer due to the narrow space. While not very apparent in this photo under bright lighting the coil fins appeared to have some caked on dust.

To clean the evaporators coils with a bench brush:

  • Have a bucket of clean water to rinse the brush.
    Best to buy a new bucket that hasn’t been used to mop the floors so there’s no residual chemicals or dirt.
  • Spray the coils with the cleaning solution.
  • Work slowly and carefully. It’s cramped and awkward work inside the coils.
  • Brush in straight lines up and down only inline with the fins.
    Never brush across the fins because you may fold and bend the fins blocking the air flow!
  • Use a light touch and brush gently, checking that you’re not bending the fins.
  • Short brush strokes are better so your movements are in a straight up & down motion.
  • Rinse the brush often in the bucket of water.
  • Spray both sides of the coils with cleaning solution again to wash off the loose dirt.
AC Evaporator Coil Interior Cleaning with Brush

AC Evaporator Coil Interior Cleaning with Brush

I’m pressing the brush downward into the fins to get at the worst of the caked-on dust where the airflow is strongest above the blower fan:

Cleaning AC Evaporator Coils with a Brush

Cleaning AC Evaporator Coils with a Brush

The brush did a really good job picking off the chunks of dirt and debris. The long bristles easily reached into the narrow top of the A-frame coils. When I took the bucket outside into the sunshine the water looked way more brown colored than this photo:

AC Evaporator Coil Cleaning - Brush and Dirt

AC Evaporator Coil Cleaning – Brush and Dirt

Here’s the A-Frame coils after cleaning and brushing with a good view of the narrow slot at the top of the coils. There’s still some brownish looking dust at the lower rear of the coils. I sprayed and brushed as hard as I thought possible without bending the fins but it wouldn’t come off. Upon closer inspection the dirt is a very fine layer that appears to be baked on the fins probably by the furnace heating during the Winter months. The spaces between the fins are clean and open for good airflow:

AC Evaporator Coils after Inside Cleaning

AC Evaporator Coils after Inside Cleaning

The Before and After cleaning and brushing the coils for comparison:

AC Evaporator Coils Before and After Cleaning

AC Evaporator Coils Before and After Cleaning

Very Dirty Evaporator Coil Cleaning

If your coils are really dirty and coated with a heavy mat of dirt then you should:

  • Soak the coils with the cleaning solution.
  • Brush off the worst of the dirt and mold, rising the brush frequently.
    Better the clumps of dirt go in the water bucket instead of the clogging the condensate drain pan.
  • Spray the coils often with cleaning solution followed by more brushing.
  • Remember to spray both sides of the coils with a heavy stream to wash out dirt between the fins.
  • Shine a flashlight through the coil fins onto a hand mirror on the opposite side to verify the air passages are open.

I finished by spraying the coils and coil case insulation with Lysol spray to kill any mold.

Reader Feedback

Don the creator of EditThis.net e-mailed me about his very dirty AC evaporator coils:

Hello Bob,

I am emailing in regards to AC coil cleaning. I went over your articles on that and they have helped me a lot but I have some questions I thought I would ask before I continue on with the cleaning.

Recently I noticed our AC was not draining the water like it should and it was draining from other areas of the AC especially near the bottom. I was told something has clogged up the drain pan etc. I thought I would open it up and took a look. Sure enough the drain pan does look like it can use some cleaning but then I noticed the A-Frame evaporator coils and the insides of them are very bad. The outsides are not too bad though. Below is a picture of the very dirty coil.

My question is, would a simple air condition coil foaming cleaner like the AC-Safe one from HomeDepot be helpful based on the condition of the coils in the image?

Look forward to your email! Much appreciated!
Thank you,
Don

Dirty AC Evaporator Coils

Dirty AC Evaporator Coils

My reply to Don was an aerosol can foaming cleaner wouldn’t work because the dirt and mold has to be mechanically removed with a brush and pump sprayer using a professional grade coil cleaner. I asked Don how long it took him to clean his coils and to send a picture of the cleaned coils:

Hi Bob,

Thank you very much for your advice! Because of your very informative website on coiling cleaning and your advice, I have managed to get the coils cleaned pretty good! Below is an image of the finished work. It may look like a lot of the fins are bent, but that’s from the flash of the camera. However, there were fins that were/are bent as you can see some in the image below. I also purchased a fin repair tool and did my best in trying to straighten out much of the bent fins. Anyhow, it was the best I can do with that. It’s a pretty good furnace/air conditioner by the way.

I’ve been meaning to get back to you on this a few or so days ago. Once again, thank you very much!

It took me a good amount of cleanings. I lost count to be honest. lol. I went the extra mile on it to do my best to be as thorough as I can. I’d say hours-wise… I spent about a good 2 – 3 hours or so with breaks here and there, etc. I got it clean well in about an hour in or so but I decided to keep at it while I’m able to, etc.

Once again, thank you!
Don

Interior AC Coil Cleaning

Interior AC Coil Cleaning

Another reader, Lauren, sent me this message and photo of her evaporator coils:

Hi Bob,

I’m a 30-year-old mother of two toddlers and my air conditioner stopped blowing cold air today. I found your website, followed the instructions, and cleaned the coils. Attached is a picture. It was disgusting! But, it’s blowing ice cold now.

Thank you for the time and effort you’ve put into your site. You saved me time and money!

AC Evaporator Coils - Interior Clogged with Dirt and Mold

AC Evaporator Coils – Interior Clogged with Dirt and Mold

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The evaporator coil front cover plate is re-installed in Close and Seal the Evaporator Coil Case.

Hope this helps,

Bob Jackson

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