What Causes an Evaporator Coil to Freeze?

Nothing works harder to keep you cool during the warm months than your air conditioner. Sometimes, however, your air conditioner might get a little too cool, causing the system not to function properly. One of the most common components in an AC unit that freezes is the evaporator coil. But what is an evaporator coil, and why does it freeze? And is there anything you can do about it?

What is an evaporator coil?

The evaporator coil of your air conditioner is one of the primary components in the heat exchange process, which allows your system to heat and cool your home. As your AC unit pulls in the warm air from your home, it passes over the evaporator coils. The coils contain liquid refrigerant that turns into gas once it interacts with warm air particles. This process quickly cools the air, which the blower fan sends throughout your home. In simpler terms, the coils hold the cold refrigerant and remove the heat from the air as it passes over them. For heating, the process is essentially reversed, creating heat from the air and pushing it into your home instead of removing it.

The 6 Most Common Causes of Frozen Evaporator Coils

1. Lack of Airflow

As stated above, the evaporator coils absorb heat from the air. But if they don’t have enough heat to absorb, the condensation on the coils can freeze. Low airflow can be caused by dozens of problems within the AC system, such as a malfunctioning blower fan, dirty air filters, or even damaged ductwork.

2. Dirty Air Filter

A dirty air filter creates the same airflow problem mentioned above, preventing the evaporator coils from absorbing the necessary amount of heat from the air to function properly. Dirty air filters can also spread dirt and clog up other parts of your system, including the coils themselves.

3. Dirty Evaporator Coils

If your evaporator coils collect too much dirt or debris, the heat exchange process can become obstructed. Dirty coils will be unable to properly absorb the heat from the air, causing the condensation to become too cold and freeze.

4. Refrigerant Problems

Ironic though it may seem, having low refrigerant in your system can actually lead to frozen evaporator coils. Low refrigerant causes the system to overwork, leading to condensation on the coils freezing. AC units work on a closed system, meaning refrigerant doesn’t simply run out. Therefore, if you have low refrigerant, the problem is either a refrigerant leak in your system or an insufficient charge.

5. Outdoor Temperature Is Too Low

Similar to how the coils freeze when there is restricted airflow, they can also freeze if the temperature of the air your system is trying to cool is too low. Since the coils absorb heat from the air, the lack of such heat can lead to condensation on the coils freezing over.

6. Clogged AC Drain Line

Condensation forming on the evaporator coils is part of normal operation. However, if the AC drain line is clogged or otherwise hindered, too much condensation may develop on the coils, which can then freeze.

How to Fix a Frozen Evaporator Coil

While many evaporator coil problems will require professional inspection and repair, there are some things you can do on your own.

Thaw the Coils

The first thing you should do is to let the coils thaw by turning the AC system off. Depending on the particular situation, the coils could take up to 24 hours to thaw on their own. You can also speed this process up by turning the system to “fan only.” This setting allows warm air to blow over the coils without the refrigerant cycle. If there is a significant amount of ice, you’ll want to have materials available to catch the water so that it doesn’t harm other parts of the system — or simply make a mess.

Replace the Air Filter

If you notice that the air filter is clogged or dirty, that might be the cause of the problem. Simply install a new filter, wait for the system to thaw completely, and resume function. If problems persist, call a professional.

Clean the Coils

While this may be a task better suited for a professional technician, you can clean the evaporator coils yourself if you are a confident DIYer.

Step 1. Turn the AC system completely off, preferably at the panel and the breaker.

Step 2. Locate the coils. They will be housed in the air handler near the blower fan. You may need to consult the manual or other resources if you have trouble finding them.

Step 3. Fill a spray bottle with a mixture of warm water and regular household cleaning detergent.

Step 4. Spray the solution and let it sit for up to 10 minutes.

Step 5. Gently wipe away the debris from the coils with a soft cloth.

Call a Professional

While there are several remedies you can perform on your own to alleviate frozen evaporator coils, you may not be aware of other issues with your AC unit. Trusting the job to a licensed professional not only gives you peace of mind that the work is done correctly, but you can also be confident knowing that they will catch any surrounding issues. 

How Preventative Maintenance Can Help

While regular wear and tear is part of any AC unit’s lifespan, preventative maintenance is one of the most effective ways to ensure your system works properly. This includes changing your air filters regularly (every 60-90 days, as a general guide) and having a professional technician inspect and tune up your system — at least annually, but we recommend having this done before the summer and before the winter months each year.

If You Need AC Repairs, We Can Help

At Complete Air Mechanical, we have experienced HVAC professionals who can inspect and repair your air conditioner. We provide services in Orange, Osceola, Seminole, and Volusia counties, and offer financing options.

Call us today at (407) 915-0144 or schedule an appointment online.