How to Unfreeze Your AC: What to Do If You Have a Frozen Evaporator Coil

September 13, 2018

Stuck with a frozen evaporator coil?

Frozen evaporator coils not only make it harder for your air conditioner to cool your home, they can also damage expensive components like the compressor.

To avoid costly damage to your system (and high energy bills), follow these steps:

Turn your thermostat from COOL to OFF
Switch the thermostat FAN setting to ON
Check your air filter
Call a professional to fix frozen evaporator coil issues

We’ll walk you through each step, and we’ll explain a few issues that could be causing your AC to freeze up that a professional needs to fix…

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Follow these steps if you have a frozen evaporator coil:

Step #1: Turn your thermostat from COOL to OFF

To prevent damage to other AC components, you’ll want to switch your thermostat from COOL to OFF.

Switching your thermostat OFF gives the super cold refrigerant (which is responsible for your AC freezing up in the first place) a chance to thaw out.

Step #2: Switch the thermostat FAN setting to ON

To help the ice on the frozen coils melt, the next thing you’ll want to do is switch the FAN setting to ON instead of AUTO.

Switching the blower fan to ON will bring in a constant flow of warm air across the evaporator coils, which will help melt the ice.

Note: Don’t leave your thermostat set to ON all the time—it’s an energy waster. When your AC is functioning properly again, you’ll want to switch it back to AUTO.

Step #3: Check your air filter

One of the most common causes of a frozen evaporator coil is, believe it or not, a dirty air filter.

You see, when a filter gets clogged with dirt and debris, it limits the amount of warm air that can pass through your air handler (where your evaporator coil is located, pictured below).

evaporator coil in air handler — *Normally, warm air blows over the evaporator coil. But if a dirty filter is blocking airflow, the refrigerant will get too cold and cause moisture to freeze on the coils.*

If no warm air is blowing over the evaporator coil, the refrigerant inside the coil will get too cold. Once refrigerant gets too cold, condensation (moisture from your home’s warm, humid air) will start to freeze on the evaporator coil.

So, if your air filter is dirty, replace it. Then wait 3–4 hours to give your coils a chance to thaw out.

After 3–4 hours, run your AC as normal again (switch your thermostat to COOL and AUTO) and see if that fixes the freezing problem. If your air conditioner still freezes over, repeat steps 1–2 and call a professional to help.

Step #4: Call a professional

If you’ve tried steps 1–2 and your AC is still freezing up, it’s time to call a professional for help because it means you need an AC repair only a professional can fix…

Problems that require a pro’s help

When you contact a pro to inspect your AC and figure out what’s causing your evaporator coils to freeze over, the tech will look for 2 types of issues.

1. Airflow issues

If not enough warm air is blowing over the evaporator coils, the refrigerant in the coils will get too cold, which will cause condensation in the warm air to freeze on the evaporator coil.

Examples of airflow issues include:

Dirty coils
Damaged blower fan
Blocked ducts
Closed dampers
Obstructed return vent
And more

2. Low refrigerant

If your air conditioning system has low refrigerant levels, the pressure in your refrigerant lines will change which can cause your refrigerant to get really cold.

Once your refrigerant gets too cold, your evaporator coil will start to ice up.

If your AC is low on refrigerant, it usually means you have a refrigerant leak somewhere in your AC system. A professional will need to find and repair this leak.

Learn more about refrigerant leaks by reading our article, “5 Signs Your Home's AC is Low on Refrigerant.”