The part(s) or condition(s) listed below for the symptom Central air conditioner 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.
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Central Air Conditioner Not Running? Central Air Conditioner TroubleshootingThe 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.
A start capacitor is often used to cycle on the compressor. If the capacitor burns out, the compressor may not run. The start capacitor can be tested with a multimeter to determine if the component can successfully hold and release its charge. If the capacitor is unable to hold and release a charge, or is bulging or leaking, the capacitor will need to be replaced.
The furnace 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 condensing 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.
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.
The capacitor provides voltage to the compressor to start it. If the capacitor is defective, the compressor won't 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.
A filter drier helps to keep the refrigerant used in the condensing unit's sealed system clean and it also helps to remove moisture from the system. Although not usually the cause of a sealed system failure, the filter drier should be replaced any time the sealed system is compromised, such as when a compressor or evaporator is replaced, or when a refrigerant leak needs to be repaired.
