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.
The air filter should be checked and replaced at least twice a year, more often in dusty/dirty environments. A clogged air filter will greatly reduce the air flow of the furnace or air handler blower which can contribute to the indoor unit's coils frosting up.
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.
Since the blower motor is the component that circulates air through the home's venting, a defective blower motor could result in the indoor unit's coils frosting up. You can use a multimeter to test the blower 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 blower wheel by hand. If the wheel does not turn freely, it's likely the motor bearings have seized and the blower motor will need to be replaced.
If the 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.
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.
Over time, the blower wheel and housing can become clogged with dust and debris. This will restrict the air flow which could result in the indoor unit's coils frosting up. You can try cleaning the blower wheel with compressed air or with a soft bristle brush. Use caution when trying to clean the blower wheel as the fins are sharp and can be easily damaged. If the blower is damaged, it will need to be replaced.
As the outdoor temperatures get colder, the outdoor coils can start to freeze up more often. When the coils frost up, a defrost control board or thermostat will energize a reversing valve to divert the warmer refrigerant from the indoor coil to help melt the excess frost from the outdoor coil. If the defrost thermostat is defective, the frost on the outdoor coils may be unable to melt. To determine if the defrost thermostat is defective, use a multimeter to test it for continuity. If the defrost thermostat does not have continuity when it reaches the low temperature of its operating range, 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.
A temperature sensor monitors the temperature of the outdoor coils. If the coils begin to frost over, the sensor will alert the defrost control to allow power to energize a reversing valve to divert the warmer refrigerant from the indoor coil to the help mel the excess frost from the outdoor coil. If the temperature sensor is defective, the defrost system will not be alerted to the excess frost.
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.
An open humidifier damper will let air bypass the indoor unit's evaporator coil. This loss of air flow can cause the evaporator coil to freeze up. If you have a humidifier on your indoor unit, confirm the humidifer damper is in the "summer mode" or closed position.
As the outdoor temperatures get colder, the outdoor coils can start to freeze up more often. When the coils frost up, a defrost control board or thermostat will energize a reversing valve to divert the warmer refrigerant from the indoor coil to help melt the excess frost from the outdoor coil. If the defrost control board is defective, the frost on the outdoor coils may be unable to melt. Before replacing the defrost control board, first confirm the reversing valve and defrost thermostat are functioning. If the reversing valve and defrost thermostat are working properly, the defrost control board is likely defective.
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.
Since the condenser 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 condenser 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.
Some air registers have adjustable louvers that allow the air flow to be restricted or shut off entirely. This would be used to cut off the air flow to a room that isn't being used, or to restrict air flow to one room so more air will flow to the other rooms. Low air flow can contribute to the inside unit's coils frosting up. If there is low air flow, check that the louvers are fully open.
Over time, the blower wheel can become clogged with dust and debris which could result in the indoor unit's coils frosting up. You can try cleaning the blower wheel with compressed air or with a soft bristle brush. Use caution when trying to clean the blower wheel as the fins are sharp and can be easily damaged. If the blower wheel and housing is damaged, the assembly will need to be replaced.
