Dirty Evaporator Coil? How to Clean an AC Evaporator Coil

The evaporator coil in your furnace or air handler is essential to effective and efficient air conditioning – and heating too, if you have a heat pump.

Can you clean evaporator coil without removing it? Yes, and we’ll discuss technique, tools and cleaner in this post.

This post gives step-by-step evaporator coil cleaning. After that, the cause and impact of a dirty evaporator coil are discussed.

Here’s the overview. We’ll detail each step in the next section.

How to Clean an AC Evaporator Coil

1. Turn off the AC by switching the thermostat to “Off.”

2. Remove the Access Panel on the furnace or air handler to expose the coil.

3. Spray no-rinse evaporator coil cleaner onto the fins – follow instructions on the spray cleaner can.

4. If necessary, use a gentle nylon brush or paint brush along with the cleaner to remove stubborn debris.

5. Once the coil is clean, replace the Access Panel and turn the AC on at the thermostat.

Those are the basic steps to give you an idea of whether you want to tackle the job or call a local heating and cooling company to do it.

HVAC companies charge anywhere from $60 to $150 or more to clean a coil, inspect the system and provide other basic maintenance.

Coil Cleaning Details

Just so we are on the same page, this is about how to clean ac evaporator coils inside house. It’s  the coil in your furnace or air handler.

There is a coil in the condensing unit outside. That coil, naturally, is called the condensing coil. It can be cleaned in much the same manner – and should be – in order to keep the entire AC or heat pump system running efficiently.

OK – If you’ve decided to DIY, these steps provide more instructions and tips on how to clean evaporator coil without removing it to ensure the job is done properly.

1. Turn off the AC by switching the thermostat to “Off.”

You certainly don’t want the system turning on while you’re working on it. It wouldn’t be dangerous, just a nuisance.

Most thermostats have Cool / Off /Heat positions. Turn the switch to Off, and you’re ready to go.

Pro Tip: The AC will need to be Off for about an hour. If you’re cleaning the compressor in summer, get an early start, so it will be back in business during the warmest part of the day.

2. Remove the Access Panel on the furnace or air handler to expose the coil.

Some panels are held on by screws, and you’ll need a Philips screwdriver to remove them. Put the screws where you won’t lose them!

Other panels have twist levers or knobs. Keep one hand against the panel while you loosen the knobs to prevent the panel from falling.

A few panels snap into place. There are tabs on the bottom of the panel that fit into slots in the furnace cabinet. Gently pull the panel toward you from the top until the snaps pop loose. Then grasp the panel sides, and lift it up and out.

Pro Tip: Some panels are sealed with aluminum foil tape to stop air leaks. Whether your furnace does or not, you might want to use it to seal your furnace panel once you’ve cleaned the coil.

The foil tape will prevent heat loss and also the “whistling” sound some furnace panels make as air is sucked through them. Plus, if you’re like us, you’ll find many uses for it around the house and garage.

hvac sealing patching tape

What does the coil look like? It has fins on it like a radiator or the back of a window AC. Copper or aluminum refrigerant tubing is welded to the inside of it. Coils come in A-shapes and N-shapes (aka Z-shape) and others too.

A Coil - 

A type coil

N Coil -

z or n type coil

Other - 

slab coil

Cased and uncased coils: If you have a cased coil, it is in its own cabinet. You’ll have to remove screws to access the fins of the coil.

Cased coil -

cased coil

Pro Tip: You might have to remove screws and a metal piece to access the interior of the coil. This video shows how it is done and why cleaning the coil on the inside is so important. It can be really dirty in there!

3. Spray no-rinse coil cleaner onto the fins – follow instructions on the spray cleaner can.

There are a couple types of evaporator coil cleaner, but the most convenient and effective is foaming cleaner that doesn’t need to be rinsed.

Frost King ACF19 coil cleaner is pretty cost-effective. It is highly rated too. It’s a no-rinse coil cleaner that can be used on the outside coil too.

frost king air conditioner coil cleaner

The Frost King product includes corrosion inhibitors to help prevent coil degradation. It is also safe for furnaces and air handlers with plastic drain trays.

Nu-Calgon 4171-75 Evap Foam No Rinse cleaner is a little stronger and might be a better choice if its been a while since you cleaned the coil and/or you have pets. Pet hair and dander can really stick to coils and bog down airflow, which reduces efficiency and can cause mechanical failure to an overworked system.

The Nu-Calgon evaporator coil cleaner is just as highly rated, but a little more expensive. It also has corrosion inhibitors, and the manufacturer states that, “it is safe for use on metals and other materials.” We can’t guarantee it’s OK for a plastic drain pain. Spray it on a piece of cheap plastic, and let it sit overnight. If the plastic isn’t damaged, it’s likely safe.

Pro Tip: Be sure the cleaner you select is usable indoors. Some coil cleaner has harsh chemicals and is suitable for outdoor use only. The Frost King and Nu-Calgon products are indoor-safe.

How it works: Spray a moderate coating of cleaner onto the coil. It will foam up and begin to break down the grease and grime. As this happens, the foam will decrease, and the liquid will run into the drain pan.

Apply a second coat after 15-20 minutes or when it appears all the cleaner has run off.

There is no need to rinse the coil.

This video from Lennox shows Nu-Calgon Evap Foam at work with an explanation of how and why to use it.

Tip for Pet Owners: Some homeowners with pets use compressed air to remove pet fur from the coil before applying cleaner. If you have a compressor and want to try this technique, blow the air the opposite way the air normally flows. In short, blow the air from the clean side to the dirty side.

4. If necessary, use a gentle coil brush or paint brush along with the cleaner to remove stubborn debris.

If debris is firmly stuck to the coil and the first round of cleaner doesn’t remove it, use a gentle brush.

Coil brushes are made in the right size and with soft enough bristles for evaporator and condenser coil fins.

This PLXparts 2-pack HVAC coil fin whisk brush is just the right size, and you can trust it not to hurt the fins. Gently work away the built-up debris. Avoid scrubbing.

evaporator fin brush

Then apply the second coat of cleaner. If used in the proper amount (see can instructions), there should be two or more coatings worth of cleaner in each can.

5. Once the coil is clean, replace the Access Panel and turn the AC on at the thermostat

Once the coil is clean, put back the inside cover, if one was removed, and put the access panel back onto the cabinet.

Remember our tip about using foil tape to seal the cabinet. You’ll save yourself a few bucks per month on your utility bill, and the roll of foil tape will pay for itself.

Why Cleaning the Evaporative Coil is Important

Heat and humidity.

The evaporator coil is key to removing those nuisances from the air in your home. A dirty coil greatly restricts airflow and causes issues with heat and humidity. Here are the details.

Heat

The coil is the part through which heat from your home is absorbed by the refrigerant and pumped and dumped outside. It is connected to a similar coil in the outdoor condensing unit. Tubing carries refrigerant pumped by the compressor in the condensing unit.

The refrigerant absorbs heat indoors when it evaporates inside the evaporator coil. It dumps the heat in the condenser unit when it is compressed/condensed back into a liquid. Heat pumps work the same way, but in reverse, collecting heat outdoors and pumping it inside.

It’s a fascinating process. But if the coil is covered in dirt, pet fur or human hair and general grimy debris, the heat transfer will be dramatically reduced.

As a result of the reduced airflow, heat won’t be absorbed as readily. That means your AC will become less effective or worse.

  • Your energy costs will rise. If you see your bills going up more than expected, then a dirty coil is a likely culprit.
  • The AC will work harder. If you AC runs more than you expect, the coil is probably dirty. An overworked air conditioner compressor and other parts are far more likely to fail. A failed compressor is generally the end of your AC condensing unit and comes with a bill of $1,200-$3,000. Sometimes more.

See our AC & Heat Pump Repair Cost Guide for details.

Humidity

The second thing the evaporator coil does is condense moisture out of the air so it can be drained away.

As the refrigerant and coil remove heat from the air moving over it, the coil’s surface gets nearly ice cold. As you know, humidity condenses on cold things.

There are two humidity problems with a dirty coil.

Higher humidity: Less airflow means less moisture condensing on the coil. The result will be air in your home that is more humid and less comfortable. In fact, as the AC works harder and harder to get rid of heat, the air in your home might become cool and clammy. Not pleasant.

Mold: Moisture, dirt and debris form an environment where mold spores will accumulate and grow. Does the air around your furnace or coming out of the grates smell musty? It’s probably mold on the coil, as shown in this picture.

dirty evaporative coil
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