- No matter what malfunction or problem causes frost and ice to gather on an air conditioning unit, the surface of the evaporator coil must reach below 32 degrees Fahrenheit for this to happen, says Inspectapedia. A number of problems can lead to a colder than normal evaporator coil. This coil normally stays cool due to refrigerant because it cools air that is blown around it, creating the cooled air your air conditioner pumps into the home.
- If you're running an air conditioning unit during the fall or winter to keep humidity low you may freeze the unit. When temperatures outside are only 40 degrees Fahrenheit, it is easy for the evaporator coils or the refrigerant lines to fall below 32 degrees Fahrenheit and accumulate frost. Try using a dehumidifier instead of your air conditioner when temperatures drop below 60 degrees Fahrenheit, recommends Horizon Services.
- Warm air blows past the cooled evaporator coils to produce chilled air. As the temperature change occurs, the surface of the coil stays above the freezing point. Dirty or clogged air filters prevent sufficient air flow, according to the HVAC Oracle, letting temperatures drop below freezing. In many cases cleaning or replacing the air filters in your air conditioning system will prevent another freeze-up. Any other cause of low air flow, such as a broken blower or debris blocking the fans, will also lead to frost buildup.
- If the thermostat in your central air conditioning system or window air conditioner breaks, it may continue to send a request for cold air even when your home is already comfortable, says Inspectapedia. This extra strain on the unit leads to frost-covered coils as they continue to fill with refrigerant and become colder and colder. Check that your air conditioning isn't running continuously when it is set to cooling mode. If it is, have the thermostat tested.
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