The part(s) or condition(s) listed below for the symptom Heat pump coils frosting up are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
If the run capacitor is defective, the fan motor may fail to run which could result in the coils frosting up. To determine if the run capacitor has failed, test the capacitor with a multimeter. If the capacitor is unable to hold and release a charge or is bulging or leaking, replace it.
If the dual run capacitor is defective, the fan motor may fail to run which could result in the coils frosting up. To determine if the capacitor has failed, test the capacitor with a multimeter. If the capacitor is unable to hold and release a charge or is bulging or leaking, replace it.
Since the condenser fan motor is the component that circulates the air through unit to cool it, a defective motor could result in the coils frosting up. You can use a multimeter to test the condenser fan motor for electrical continuity, a continuous electrical path present in the motor, as well as determine if power is reaching the motor. You can also try turning the fan blade by hand. If the blade does not turn freely, it's likely the motor bearings have seized and the motor will need to be replaced.
Since the fan motor is the component that circulates the air through unit to cool it, a defective motor could result in the coils frosting up. You can use a multimeter to test the fan motor for electrical continuity, a continuous electrical path present in the motor, as well as determine if power is reaching the motor. You can also try turning the fan blade by hand. If the blade does not turn freely, it's likely the motor bearings have seized and the motor will need to be replaced.
If the outdoor coil is clogged with debris, the fan will not be able to move air through the coil, resulting in the coils frosting up faster. The coil can be cleaned with a garden hose and spray nozzle from the inside out. If the coil is excessively dirty, a coil cleaner spray can be used to help loosen the dirt. Inspect the furnace or air handler air filter and replace it with a new one if the filter is dirty or hasn't been changed in the past six months.
Since the fan blade is the component that circulates the air through unit to cool it, a damaged or defective fan blade could result in the coil icing up. Inspect the fan blade for any damage or wear and confirm it can spin freely on the condenser motor shaft. A visibly damaged or worn fan blade should be replaced with a new one.
If the system is low on refrigerant, the compressor may not be able to generate enough heat at the indoor coil to melt the frost when the reversing valve energizes in the defrost cycle.
