The part(s) or condition(s) listed below for the symptom Heat pump compressor won't run 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.
A run capacitor will power either the compressor or the fan motor (a dual run capacitor will power both). If the capacitor burns out, the compressor may not run. 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.
A capacitor will power either the compressor or the fan motor (a dual run capacitor will power both). If the capacitor burns out, the compressor may not run. 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.
A dual run capacitor will power both the compressor and the fan motor. If the capacitor burns out, the compressor may not run. To determine if the dual 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.
The control board sends a low voltage signal to the contactor. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the outside unit components. If the contactor is defective, it can prevent the compressor from running. To determine if the contactor is at fault, use a multimeter to test the contactor coil for continuity. If the contactor coil does not have continuity or the contacts a on the coil look burnt, replace it.
The compressor is a pump which compresses the refrigerant and circulates the refrigerant through the evaporator and condenser coils. If the compressor is defective or worn out, it likely won't run. However, this isn’t usually the case. Before replacing the compressor, first check all of the more commonly defective components. If all of the other components are working properly, use a multimeter to test the compressor for continuity. If there is an open circuit, the compressor is likely defective.
If the heat pump unit contactor is not receiving 24 volts or power is not getting to the inside blower motor, a possible cause is a defective furnace or air handler control board. While this is not a common problem, if all other potentially faulty components are working properly, the control board should be replaced.
The control board sends a low voltage signal of 24 volts to the contactor through the wall thermostat. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the outside unit components. There should be 24 volts between the common (“C”) and yellow (“Y”), and common ("C") and orange ("O") thermostat wire terminals on the air handler control board when the wall thermostat is in the heating mode. You can check for this voltage with a multimeter. If voltage is not reaching the contactor or reversing valve, it's likely the wall thermostat is defective and will need to be replaced.
The control board sends a low voltage signal of 24 volts to the contactor through the WiFi thermostat. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the outside unit components. There should be 24 volts between the common (“C”) and yellow (“Y”), and common ("C") and orange ("O") thermostat wire terminals on the air handler control board when the WiFi thermostat is in the heating mode. You can check for this voltage with a multimeter. If voltage is not reaching the contactor or reversing valve, it's likely the WiFi thermostat is defective and will need to be replaced.
The air handler needs to have power reaching it for the heat pump unit to run. If the furnace or air handler control board has an indicator light, confirm the light is illuminated which indicates power is present. If there is no power to the furnace or air handler, check the home's circuit breaker or fuse. Confirm the power switch on the side of the furnace or air handler is turned on.
The outdoor heat pump is energized with 240 volts of electricity. The electricity flows through a disconnect box to the compressor and outdoor fan motor. The disconnect box enables the outdoor unit to be turned off outside. The disconnect box includes a cartridge which may contain fuses. If the compressor and condenser fan motor do not run, the disconnect box fuses may have blown, or the circuit breaker that supplies power to the disconnect box may have tripped. To determine if the disconnect box fuses have blown, use a multimeter to test the fuses for continuity. Fuses that do not have continuity should be replaced.
