Troubleshooting Frozen Evaporator Coils

Most homeowners don’t realize there is a problem until they see that the unit runs continuously, the temperature is too warm, or there is reduced airflow. When people here the hum of the blower and compressor running, they assume it is working. If they happen to go outside and see ice on the line coming out of the home, they might become concerned. The real cause for the reduced capacity is that the evaporator coil, the one inside the air handler, is either partially or completely frozen preventing any air from getting through. To see this you would have to remove an access panel on your unit to inspect the coil. If you go to the air handler you may notice the area where the coil is located may be sweating due to the ice inside coming in contact with the metal casing of the unit or plenum. The condensate drain may also be sweating from the colder than normal temperatures. In extreme instances, ice will begin to form on the outside of the unit.

What To Do

The best thing to do once you notice your air conditioner is frozen is to turn it off. If it is summer and you have a frozen heat pump system you can turn it to the heating mode and it will pump hot refrigerant through the coil to accelerate the defrosting process. If an excessive amount of ice is on the evaporator coil, defrosting the frozen coil may overflow the condensate drain and you may have some water damage. This may happen on any type of system if the air handler is located in a hot attic. For standard AC systems, go to the thermostat and turn the air conditioner to the off position and turn the fan switch to on or manual at the selector switch on your thermostat. This will help defrost the frozen evaporator coil and by blowing warm room air over the coil.

On manual thermostats the selector switch is on the bottom or side to place the fan to ON

Also note that a heat pump will form frost or ice on the outside condenser coils in the winter which is common and most heat pumps are equipped with a method to defrost the condenser coils.

What Not To Do

Dirt or dust accumulation on the surface of your coils can inhibit heat being transferred. This can the coil to run too cold and freeze. Most evaporator coils are sealed and not a good project for do-it-yourself methods. Coil inspection and cleaning is a standard part of regular annual maintenance by an HVAC service provider.

If you notice that your evaporator coil has frozen over, contact an AC Repair so they can find the source of the problem. It’s helpful if you turn off your air conditioner before they arrive at your home so that it can defrost before they arrive. After the source of the problem is discovered, they will fix it and advise you on how to avoid it from happening again!