● Dirty air conditioning filter can block or reduce air flow across the cooling coil, leading to coil frost. This is the first component a homeowner should check since the cleaning and replacing the air filter, is so easy.
● Dirty blower fan blades or non-functioning blower fan assembly: an air handler blower unit that is not moving as much air as it should will be blowing too little air across the evaporator coil. This is a less likely but possible cause of frost build-up on the cooling coil.
● Debris-blocked evaporator coils might lead to evaporator coil icing: When an air conditioning or refrigeration unit evaporator coil becomes sufficiently blocked with debris as to slow down the air flow enough, the coil may actually become so cold that the condensate forming on its surface freezes, completely blocking the coil.
● The refrigerant charge is too low. If there is a refrigerant leak, the first symptom may be coil icing; but later as refrigerant continues to be lost, all cooling may be lost and the coil will no longer be frosted or iced over.It's better to find and fix the refrigerant leak.
How to fix this problem :
● To fix this problem you first have to eliminate any existing ice or frost. To eliminate the ice or frost, turn the unit to Fan only(by clicking the Mode button) and set the speed to high. The unit should defrost fairly quickly ( 5 - 15 minutes). Then, run the unit in Fan mode until the coils or vents are dry or nearly dry.
● After the coils or vents are dry, turn the unit back to AC, but set the thermostat to a temperature a few degrees lower than the room temperature to start. The compressor will run until the temperature in the room reaches the set point, and then cycle off.
● When it is off, any ice that may have accumulated on the coils or around the vents melts. Over time, gradually reduce the temperature setting a few degrees at a time, so that the compressor continues to cycle on and off, until you reach the temperature you want.