5 Causes of a Frozen Evaporator Coil & What To Do About Them

If you’ve ever found your AC’s evaporator coil iced over, you probably also found that your AC was blowing out warm air, or even worse, shut down completely. 

Your frozen evaporator coil was most likely caused by a blockage of airflow which can be solved by replacing your air filters or cleaning the evaporator coil. In other cases, your AC may be low on refrigerant, in which case you’ll need to call an HVAC professional to refill your system.

In this article, I’ll go over what could be causing the evaporator coil to freeze and go over in more detail how you can try to fix the problem yourself before calling a professional. 

What Is an Evaporator Coil

The evaporator coil is the part of your air conditioner that absorbs heat from the surrounding air so it is essentially one of the most important parts of the cooling process.

When you turn on your AC unit, the compressor starts up and pushes the warm air out of your house. Once the air leaves your home, it passes through the return ducts, into the AC unit, and over the evaporator coil.

Evaporator Coil of an AC

The coils are filled with liquid refrigerant which absorbs the heat from the air as soon as the air passes over it. During this process, the refrigerant is converted from a liquid into a gas, and the blower fan sends the cool air back into your house. 

So in other words, without a properly functioning evaporator coil, there would be no cool air. 

Signs That Your Evaporator Coil Is Frozen

The most common sign of a frozen evaporator coil is visible ice and frost on the coils. You may even see ice buildup on the pipes going in and out of the AC unit. But sometimes you don’t see any visible ice on the outside of the unit and something is clearly wrong with your AC.

If you notice that your AC is not working at all, or only blows warm air, then you should check for signs of a frozen evaporator.

Another thing to look for, especially if you have a window unit, is condensation dripping onto the floor. This could happen when the evaporator coil is too cold and water is being forced out of the system instead of being absorbed by the coils.

A loud buzzing noise or any unusual sounds coming from your AC unit is another tell tale sign that something is wrong. 

What Causes an Evaporator Coil to Freeze

When the evaporator coil freezes, the entire cooling system stops working. It’s something that we see happen quite commonly. Think of your AC unit as one continuously flowing system. If one part of the system is blocked or goes down, the rest of the system won’t be able to function properly.

I wouldn’t recommend leaving the coil frozen for too long or else you could have to deal with damaged coils or worse, a damaged condenser. 

So when you discover that your evaporator coil is frozen, the first thing you need to do is unfreeze the coils. Turning off your AC unit and giving it time to thaw out should do the trick. Then, you’ll need to find the root of the problem so it doesn’t keep freezing up. 

Let’s take a look at a few common things that cause an evaporator coil to freeze and what you can do in each of those situations to avoid any further problems with your AC. 

Low refrigerant

As I mentioned above, the evaporator coil houses liquid refrigerant. It’s what absorbs the heat passing through your AC and turns it into cool air. There needs to always be a certain amount of refrigerant in the coil in order for your air conditioner to run smoothly, so I recommend checking the refrigerant levels often.

When refrigerant levels drop below normal, it will cause a decrease in pressure inside the evaporating coil which allows water vapor in the air to condense and form ice on the coils.

Man measuring the refrigerant

If you suspect that your refrigerant levels are low, you should call an HVAC technician to come out and service your system. They can check the refrigerant levels and add more refrigerant if needed. 

It’s important that you never try to refill the refrigerant yourself because for one, refrigerant is an EPA controlled substance that could cause harm if released into the environment. And two, because if you don’t properly measure it, you could overcharge the system which would backfire and cause your system to shut down completely. 

Bad airflow

Another important thing to consider when it comes to your air conditioning system is airflow.

Remember that I said the evaporator coils absorb the heat from the air that flows over them? Well, if that airflow is restricted, the evaporator coil can’t properly do its job. And without warm air continually passing over it, the coil will become too cold and that’s when it will start to freeze.

So as important as it is to keep that airflow going in order to keep the air conditioner working properly, there are several things that could obstruct that airflow, which could in turn result in a frozen evaporator coil.

Clogged Air Filter

A clogged air filter or dirty evaporator coil, which I’ll touch on in a bit more detail below, are a couple common airflow blockers. But did you know that closing your air vents in your house when you have the AC turned on can also block the airflow to your system?

That’s right! If you close all of your vents while your AC is running, it won’t allow enough air to pass through your system and that could lead to a frozen evaporator coil as well.

To prevent this from happening, make sure to leave the vents in your house open whenever you have your AC unit turned on. 

Clogged air filter

If I suspect blocked airflow is the reason the AC is not cooling properly, the air filters are usually the first thing I check. These filters are usually located near the AC unit’s intake port. They’re typically designed to trap particles like pollen, dust, dirt, and pet dander, among other things. But over time, all that pollen, dust, and debris can clog the filter and block the air from flowing onto the evaporator coil. 

Dirty Air Filter

It’s an easy fix that can be solved by changing your air filter. This is easy and you can generally do it without the help of a professional. Make sure to turn off your AC first by flipping the circuit breaker, then remove the old filter and put the new one in. The new filter will usually have arrows indicating which direction it needs to be put in.

Remember to check all parts of your AC system as sometimes there are multiple filters. Since your AC unit is a continuous flow, changing all of them is necessary to ensure proper airflow throughout the entire system. 

Dirty evaporator coil

Once you’ve inspected the filters, you’ll want to make sure that the evaporator coil itself isn’t clogged with dust and grime. A dirty evaporator coil causes the entire system to work harder to cool the air and puts the coil at risk of freezing. 

To do this, simply pull out the blower motor assembly and inspect the evaporator coil. You’ll want to look for any signs of discoloration, corrosion, or buildup.

Dirty evaporator coil

You could also do a static pressure drop test on the evaporator coil, but in my experience, a visual inspection of both sides of the coil will suffice in determining whether it needs to be cleaned or replaced. 

You can clean the coil yourself with a store-bought coil cleaner – I find the aerosol spray cleaners to be the easiest – or you can mix up your own solution of soap and warm water. After turning off your unit, spray the cleaner on the coils, give it a few minutes to soak up the grime, and then wipe it away with a soft cloth or brush. 

Blocked condensate line

Condensation lines drain moisture that is created when the evaporator coil turns refrigerant from a liquid to a gas out of the air conditioning system. When one gets clogged up, water can’t escape and that will cause your evaporator coil to freeze. It could also cause the condensate line to freeze which could cause even bigger problems for your AC system. 

Condensate Line

Mold, mildew, and other debris can often collect in the condensate lines because they’re enclosed spaces where water sits causing them to clog up. To avoid this, I recommend regularly cleaning your condensate lines.

To clean it, you’ll need one cup of distilled white vinegar and a pipe cleaner. First, turn off your unit, then remove any visible signs of blockage with your pipe cleaner, then pour your distilled white vinegar down the drain line. You can flush the line with fresh water to give it an extra rinse. I would wait about an hour before turning your AC back on.

How Expensive Is It to Fix?

Like I said before, the first thing you want to do when your evaporator coil freezes is turn off your air conditioner to thaw out the coils and remove any ice. Never try to chip ice off the coils manually because this could cause damage to the coils and end up costing you a lot more money and having to replace the coil. 

Then, go through my checklist above of possible causes that leads to the freezing in the first place and fix that problem.

Most of the problems like changing the air filters, cleaning the coils yourself, or cleaning the drain lines have simple DIY solutions that won’t cost you more than $20-$50 in supplies.

Other fixes, like refilling the refrigerant, can only be done by a professional. Freon, the most common type of refrigerant, costs about $50 to $150 per pound, so your total cost will depend on how much your system needs.

But if the freezing persists, or you don’t catch it in time and it does permanent damage to other parts of your AC system, you may get stuck with replacing expensive parts or even the entire unit. 


In conclusion, a frozen evaporator coil is a common problem among homeowners. While these problems aren’t necessarily dangerous in the beginning, they can cause your system to work harder than it needs to, which will lead to higher energy bills for you and, if left untreated, could cause serious damage to your system.

The first step towards fixing a frozen evaporator coil is to turn off the AC unit and thaw out the coils. Then find the root of the problem and repair that to avoid future freezing. 

I’ve gone over some DIY solutions to the most common causes, but a professional HVAC technician can always help inspect your system and repair the issue if you are unsure what is causing it.

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