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How to Troubleshoot Frozen Evaporator Coils

Published on: July 18, 2015
AC unit on white background | AC Southeast

Although most central air conditioners and heat pumps run dependably day after day, it’s helpful to know about troubleshooting frozen evaporator coils to prevent the loss of cooling, as well as avoid the potentially serious consequences of a frozen coil. If your air conditioner’s coil freezes and the system doesn’t shut off, it can burn out the compressor, which is the equipment’s most expensive part.

What the Coil Does

The blower motor inside the air handler pulls your home’s air over the evaporator coil, and the chilled refrigerant removes its heat. This results in cooled air that blows through the ductwork to keep your home comfortable. Anything that interferes with the amount of air going over the coil or the refrigerant level can cause it to freeze.

When It Freezes

If your A/C is running but it’s not cooling, turn the system’s power off and check the coil. It may be physically visible inside the air handler or by removing a metal cover plate. If the coil is inaccessible, contact your HVAC professional, since fixing a frozen coil often calls for technical expertise.

Blocked Airflow

The most common cause of a frozen coil is a dirty air filter that slows the amount of air blowing over it. The coil contains exceptionally cold refrigerant, and unless the airflow is at or near the manufacturer’s specifications, the refrigerant inside the coil won’t remove enough heat. A dirty filter combined with humid indoor air sets the stage for ice formation on the coil.

As water vapor in the air contacts the cold coil, it condenses. When insufficient air blows over the coil, the condensation has time to freeze instead of draining away into the condensate pan and then out through the drain pipe.

You can easily start troubleshooting frozen evaporator coils caused by a dirty filter by simply looking at the filter’s condition. If it’s covered with dust, replace it as soon as possible after turning the A/C off. Don’t run your air conditioner or heat pump without an air filter because the airborne particulates will cover all its parts, including the coil.

Another cause may be blocked supply and return registers that don’t deliver enough return air through the air handler, making the coil freeze over. If you’ve deliberately closed off some rooms in your home to save energy, you may need to open them up to increase the return airflow.

A Dirty Coil

Over time, dirt and debris can build on the coil, or it may be covered with mold or other biofilms. The coil provides a perfect environment for the buildup of mold or bacteria that will eventually cover it. Not only does this covering increase energy bills, but the microorganisms can also circulate through your home’s air, degrading indoor air quality (IAQ)and causing respiratory irritations.

If you can access the evaporator coil, look at its condition. If it’s covered with dust, use a gentle brush to remove it. You may need an HVAC professional to remove any biological growth and completely clean both the condensate pan and drain pipe, since poor drainage can prompt these growths.

Installing ultraviolet (UV) lights inside the air handler that point to the coil will prevent biological growth on both the coil and air handler. Your HVAC contractor can place these lights inside the air handler and the ductwork to improve IAQ. UV lights alter the DNA of mold spores, bacteria and viruses, preventing them from reproducing.

Low Refrigerant

Too little refrigerant in the system can cause the coil to freeze. Troubleshooting frozen evaporator coils for low refrigerant requires the expertise of an HVAC contractor who can test the pressure, trace and fix the leak, and refill the system. The Environmental Protection Agency (EPA) regulates refrigerant for HVAC systems since it poses environmental risks and only licensed technicians can handle it.

For professional help when troubleshooting frozen evaporator coils, contact AirConditioningSouthEast.com to find a trusted HVAC contractor near you today.