Photograph of a dirt blocked air conditioning evaporator coilAir Conditioning Cooling Coil or Evaporator Coil Cleaning Methods

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Air conditioner or heat pump cooling coil / evaporator coil cleaning methods:

This article discusses the how the cooling coil (evaporator coil) in the air conditioning air handler unit is cleaned. These same methods will work on the outdoor coil or condensing coil as well. Our photo at page top shows a very dirty cooling coil in the attic air handler component of a central air conditioning system.

How to clean a dirty or moldy air conditioning cooling coil or evaporator coil, or a dirty condensing coil; Use of spray foam cleaners & deodorizers on cooling coils - Use of liquid cleaners on cooling coils; Use of compressed air to clean cooling or condensing coils; Use of pressure washers or steam to clean HVAC Coils.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

How & Why Air Conditioning & Heat Pump Evaporator Coils (Cooling coils) are Cleaned

Which Cooling or Heat Pump "Coil" is Which: Condensing Coil & Cooling/Evaporator Coils Defined

The COOLING COIL or EVAPORATOR COIL discussed here is the evaporator coil found inside the air handler, used to cool air blown across it and into the building occupied space. If your concern is with If your equipment is a heat pump these terms can be a bit confusing because in heating mode, your heat pump system's indoor coil is warming, not cooling the air blown across it

The CONDENSING COIL is normally on the outdoor or compressor portion of your air conditioning system. The job of the condensing coil is to cool high temperature refrigerant gas to condense it back to a liquid refrigerant form.

Why do we clean the HVAC evaporator or cooling coil, or the condenser coil?

Dirt and debris accumulating on an air conditioner or heat pump coil block airflow across the coil, increasing the cost of heating or cooling the building. In severe cases cooling or condensing coils can become so blocked that air flow is seriously reduced, possibly also leading to an evaporator or cooling coil icing problem indoors or an overheated, damaged compressor outdoors, or simply loss of cooling capacity of the system.

In addition, a blocked evaporator coil can cause the HVAC compressor to run at higher than normal temperatures - a condition that over time can break down lubricants circulating inside the system, thus shortening the life of the compressor motor itself.

BLOCKED COOLING COIL - Air Conditioner Evaporator Coil Blocked by Debris

Photograph of a dirt blocked air conditioning evaporator coil ICE on the COOLING COIL is not the only (nor even the most common) cause of blocked air flow in an air conditioner. This photograph shows how easily debris can stick to and clog the inlet side of the cooling coil in an air conditioning system. This evaporator coil was nearly totally blocked with dust and debris. How does this happen?

There was no air filter installed in the system. Ordinary house dust is comprised largely of fabric fibers and skin cells.

These and other debris in building dust such as soot and organic particles like pollen and mold spores all join to form a gray mat on the fins of the cooling coil in an air handler.

Debris sticks particularly quickly to this surface because of the combination of close spacing of the cooling fins (about 1/16" apart) and the fact that condensate forming on the coil keeps the surface damp.

Details about the detection and cleaning of dirt and debris which block an air conditioner cooling coil are at DIRTY COOLING COIL / EVAPORATOR COIL.

Guide to Procedures for Cleaning Air Conditioner or Heat Pump Evaporator Coils: Using Air, Brushes, Chemicals, or Detergents to Clean A/C Coils

Thorough cooling coil or A/C evaporator coil cleaning can require cutting refrigerant lines, removal of the coil and other components for cleaning, and reinstallation, pulling a vacuum on the refrigerant lines, and recharge with refrigerant.

Such service and repair may involve significant expense. For this reason there are several "in place" cleaning methods using foams and sprays that are a simpler procedure for cleaning an air conditioning or heat pump coil.

Watch out: be sure that electrical power is off to the HVAC equipment before opening access panels or working on the system. Relying only on the door safety interlock switch to turn off equipment power may be unsafe as wiring inside the unit will still be "live" in some locations.

Using Air: Compressed air for cleaning HVAC evaporator coils

Some HVAC technicians clean an evaporator coil by blowing it off with compressed air. This is a quick and probably effective method to clean the coil, which has the additional feature of blowing dust, debris, and possibly mold into the building air - not something we approve.

Air is sprayed from the cleaner side of the coil towards the dirty side - or in other words, in the opposite direction from the normal air flow across the coil. Be sure to spray from the correct side of the coil or you'll just be forcing dirt and debris more deeply into the coil fins.

Watch out: if you are using high pressure air to try to clean a coil, be sure you blow air at right-angles or straight through the coil fins. Blowing high pressure air (or water or steam) at the HVAC coil fins on an angle is likely to bend over the fins, clogging the coil and possibly ruining it. If just a few fins have been bent on a coil they can often be straightened by working gently with an HVAC coil comb designed for that purpose.

Watch out: if you are not careful, just using compressed air to blow off a coil may leave a large amount of dust and debris inside the air handler where it collects anew on coil surfaces, or in your eyes (dangerous). Using a shop vac in concert with the compressed air sprayer and moving carefully (to avoid damaging coil fins) can reduce dust and debris spillover and make cleaning up easier.

Condenser coil cleaning: We don't have a complaint about using compressed air to clean an outdoor evaporator coil since we don't have the same concern about blowing debris into the building or its duct work.

Brush-cleaning of A/C or heat pump cooling or heating coils

When the coil is soiled by a fairly light coating of dust and debris, it can often be successfully cleaned using a soft brush. If you clean you A/C or heat pump coil every three or four months using this method you may reduce cooling (or heating) costs and you may be able to avoid more costly or troublesome coil cleaning procedures.

If your HVAC equipment is operating in a dusty area or if no one has been maintaining proper filters in the system it is likely that you'll need to clean the coil more frequently, perhaps even monthly to keep the A/C or heat pump system at peak operating efficiency and effectiveness.

We have tried using a shop vac with a soft brush attachment to clean the A/C coils, but if your coil is mounted in the air handler so as to not leave much room to access all of its surface this approach doesn't work well.

Watch out to avoid damaging coil fins when using any tools, brushes, or vacuum cleaners around the equipment.

Using Chemicals to Clean A/C Coils

There are plenty of coil cleaning chemicals sold for cleaning A/C or heat pump systems, both acid and alkaline-based.

Watch out: We do not recommend using strong chemicals on an A/C or heat pump coil because of the risk of corrosion damage to the coil or the production of noxious odors & fumes. To be safe, check with your HVAC equipment manufacturer to be sure that your cleaning approach is one they approve.

Indeed there are foaming cooling coil cleaners on the market that can gently lift and help remove coil-clogging debris with minimum damage to the cooling coil.

Field Report: corrosion visible after a cooling coil was cleaned

Cooling coil after cleaning (C) InspectAPedia - K.C.I just had my duct work and AC cooling fins cleaned out. After the cleaning it appeared as if the aluminum cooling fins were full of with fluffy green stuff.

[Click to enlarge any image]

I called the technicians who came back to look and then explained that what I was seeing was corroded aluminum that was more visible since the cooing fins are now clean. Although this sounds plausible I have two concerns.

1. if if is corroded aluminum do I need to be concerned about using the ducts.


2. it is not corroded aluminum and they did a really bad job at cleaning

The cleaners are part of the national duct cleaners association (NADCA), seemed quite knowledgeable and experienced (no complaints, A+ at BBB), but I am surprised that the fins look so bad. I would like to know whether what I am seeing is to be expected.

l. I did snap a picture on the one side of the "V" that was easily accessible, here it is. This is the AFTER cleaning picture, I dont have a before. The schmutz has a slightly greenish hue.

The AC handler and ductwork is old, and based on the amount of crud throughout the system appeared as if it may have never been cleaned before.(the condenser unit itself is 25+ years old, but still working). That conclusion also comes from the fact that the prior owners seemed to take pride in performing NO basic maintenance on the house for many years. I just hope that firing up the AC system in a couple weeks won't endanger my family. - Kevin 4/28/2014

thanks. K.C. 4/28/2014


In my initial reply I said "I am not sure I buy the explanation that "you only see the crud because now we've cleaned the coils". That would be the case if we saw thick green crud that was actually blocking or covering-over the coil assembly.

But now that I can benefit from seeing your photo (above left) I think that we are looking at corroded aluminum fins on the coil and that the cleaning company is being dead honest in saying you couldn't see this before - this condition would have been covered if there were a layer of thick dust and debris.

Your photo is not quite clear on the point, but if there is good air flow between the fins on the coil and presuming it's not leaking, it should be functional. This is about as good as you're going to get in cleaning this coil. It would not be likely that the coil cleaning procedure using approved methods and materials would endanger your family. (You might however want to inspect the HVAC system ductwork for cleanliness, including the air handler and blower fan assembly.)

There is some heat transfer loss where aluminum coil fins are deteriorated by corrosion, but most likely a significant gain in coil performance overall by cleaning if it was previously debris-clogged.

To understand this coil's performance better, an in-focus photograph looking directly into the coil fins - at right angles to the plane of the coil - would let us see whether or not there is open air space between the fins. Take care not to damage the fins nor cut yourself on sharp edges. It may help to try shining a light from the other side of the coil if it's accessible. If not the photograph will rely on lighting or a flash from the camera's side.

If we see open air space between the fins then the coli has been successfully as opened as we're going to get it.

Unfortunately I cannot recommend any more aggressive cleaning like brushing. The aluminum fin material is thin to begin with and is more fragile now as it has been corroded. More aggressive cleaning that bends (which means blocks) or removes (which means still more capacity loss) fin material just makes matters worse.

Replace the coil, or the whole unit, if/when the coil leaks refrigerant.

Field Report: Using Hydrogen Peroxide to Clean an HVAC Coil?

I used Hydrogen peroxide 3% to do the job and it gave a bad smell. Kind of a chemical smell. I think the peroxide reacted with the zinc,aluminum, copper or nickel metal in the cooling coils. Is it OK to use peroxide to clean cooling coils besides the conventional HVAC tech cleaning methods? I live in an apartment and sometimes my AC air starts to get a moldy smell to it.

The first time I cleaned it out myself there was all this orange yucky fungal sludge in the drip tray and there was so much of it that it had clogged the drain pipe which I had to clear out. I cleaned it out with 5% hydrogen peroxide and whatever it was it bubbled like crazy so I believe the peroxide was reacting with a biological agent. It also reacted with something between the fins of the cooling coil to give a smell slight of sulphur and burned gunpowder. What are your thoughts on the matter? - N.M.

While we have read reports that the oxide on the surface of aluminum HVAC coil parts reduces the severity of chemical reaction between an acid or base cleaner and the metal, we have also had reports of problems with corrosion and odors when this approach was tried.

So while the "bubbling" action of hydrogen peroxide is appealing as a cleaner, we are warned that chemical reactions between some coil cleaning products and the aluminum or copper A/C or heat pump coil parts can corrode the fins or tubing, damaging the system, ultimately leading to leaks and the need for a costly coil replacement.

Chemical reactions between some coil cleaning products and the aluminum or copper A/C or heat pump coil parts can also produce obnoxious odors or fumes, possibly toxic or irritating fumes, and in some cases may leave an odor in the system that itself becomes an issue.

See our discussion of detergents and foam sprays for coil cleaning, below - those are safer approaches to coil cleaning, especially if you're not an expert.

Using Detergents or Water for cleaning A/C coils

Using a simple hand sprayer or garden sprayer (these produce a gentle spray) it may be possible to clean your A/C or heat pump coil effectively using tap water or a mild detergent. The advantage of using these gentle solutions is that there is little risk of damaging the coil fins or tubing compared with the use of more harsh chemicals.

Wet the A/C or heat pump coil surfaces with your spray-on detergent, let it soak in for 15 minutes or so (but not long enough to dry out), then rinse the coil and coil fins clean. Remove spillover and debris from the condensate pan where your spray and debris land, using a shop vac or hand wiping.

Watch out: don't bang around inside the air handler with your shop vac or you may damage the evaporator/cooling coil or coil fins; and be careful when wiping by hand that you don't get cut on sharp fin edges.

If using water or a non-sudsing mild detergent doesn't work to clean off your coil, you may need to use a more aggressive coil cleaning method such as those described below.

Using Foam or spray HVAC coil and fin cleaners

Using a garden sprayer (or a sprayer that may be included in some pre-packaged A/C coil cleaning systems and products), the coils are sprayed with a foaming cleaner specifically designed for HVAC systems. An advantage of this approach is that it is mechanically gentle, reducing the risk of damage to the coil or its fins. And if you select a benign cleaner it is also chemically gentle, avoiding corrosion damage to the coil.

Where to Buy HVAC and Refrigeration Equipment Coil Cleaning Products

Advice on Choosing an A/C or Heat Pump Coil Cleaning Product: chemistry

Watch out: review your choice of HVAC coil cleaner with the equipment manufacturer and/or the cleaner manufacturer before choosing a coil cleaner, and then be sure to follow the coil cleaner's instructions. Choosing the wrong type or wrong chemistry of coil cleaner or failure to rinse off cleaners (some require rinsing) can result in costly damage to the coil and could even be unsafe.

Do not use an acidic soil cleaner on coils made of aluminum, copper, or other metal that may be damaged by the corrosive effects of the copper. Some air handlers use a plastic blower squirrel cage fan wheel that is also sensitive to acids, becoming brittle and possibly breaking from acid treatment.

Some HVAC service companies may use an acidic coil cleaner on the outdoor coil, followed by a water wash.

Some HVAC service technicians whose comments we've read or asked-for opine that plain water is perfectly adequate to clean and rinse most residential outdoor coils.

When to Use a Self-Rinsing Coil Cleaner

Some but not all coil cleaning sprays and foams require rinsing of the coil after use. Typically the outdoor coil in the compressor/condenser unit will use a coil cleaner that is followed by a rinsing step since rinsing the outdoor equipment can be practical.

Indoor coils in an air handler are usually selected from products that don't require a rinse step since rinsing with a garden hose (for example) would be impractical indoors. Cleaners that do not require an additional rinse step are typically described on their label or in their instructions as "self rinsing", typically using a slightly alkaline detergent cleanser.

How does a self-rinsing coil cleaner work? Residues from the coil cleaner are washed off of the coil fins and tubing by condensate that forms on those surfaces when the indoor unit is run in cooling mode.

That rinsing condensate is then collected in the coil condensate drip pan, routed from there to an approved condensate drain, or perhaps through a condensate pump to the drain. (CONDENSATE HANDLING, HVAC has details)

Do not Make Your Own Coil Cleaner

Do not try making your own coil cleanser out of other household cleaners like bleach, dishwasher or laundry detergent, as these may be harmful to the coil metallic fins or even its tubing.

Do not use a coil cleaner containing trichloroethylene inside buildings (such as schools or post offices) where use of those products is prohibited.

Watch out: we do not recommend use of high pressure cleaning on cooling or condensing coils. High pressure can damage delicate coil fins and can even blow off or damage sensors or electrical connectors.

List of HVAC coil cleaning chemicals, foams, and sprays:

The HVAC coil spray approach has the appeal that the total cleaning cost is low, no rinsing is necessary with some products, and the coil looks nice.

Where does the debris and run-off cleaner go? It should drip into the condensate pan for disposal through the condensate drain system. The manufacturer says the coil and fin cleaner also removes odors from the system, but if your HVAC system is quite dirty additional steps will be needed to clean the blower assembly and the ductwork.

After the coil cleaning foam has worked on the coil surfaces and dripped to the condensate pan below, use a wet-dry shop vac to clean up the mess from the pan, followed by careful wiping as we cited above.

Using Pressure Washers to Clean A/C or Heat Pump Coil Fins & Tubing

Professional HVAC service companies often use a portable A/C coil pressure washer designed for that purpose. Unlike cleaning detergents or foams, a pressure washer is physically more aggressive coil cleaning method and is perhaps the most thorough or effective method for cleaning a badly soiled or blocked HVAC evaporator or condenser coil.

A portable pressure washer unit such as Goodway's CC-140 contains both a coil cleaning solution (typically a detergent mix) and a battery-operated pressure sprayer that can deliver as much as 140 psi. Heavier-duty coil cleaning pressure sprayers are available for commercial units and larger, or heavier, wider coils.

Watch out: as we warned earlier, if you are using high pressure air, water, or steam to try to clean a coil, be sure you blow air at right-angles or straight through the coil fins. Blowing high pressure air (or water or steam) at the HVAC coil fins on an angle is likely to bend over the coil fins. And don't over-do it and don't spray more cleaner than needed - you'll just have more liquid cleanup to do after the coil has been treated.

Using Steam-Cleaning of A/C or Heat Pump Coils

Steam is used by some technicians to clean HVAC coils, in a process similar to that we described above for compressed air.

Watch out: as we warned earlier, if you are using high pressure air, water, or steam to try to clean a coil, be sure you blow air at right-angles or straight through the coil fins. Blowing high pressure air (or water or steam) at the HVAC coil fins on an angle is likely to bend over the coil fins.

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See COOLING CAPACITY, RATED of air conditioning equipment if the system seems to be working but is inadequate to cool your building.

Air Conditioner or Heat Pump Cooling Coil Articles


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