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HomeRepair HelpCentral A/C RepairCentral air conditioner compressor won't run Repair
Central air conditioner compressor won't run
When your central AC compressor won't run, the system may blow warm air or fail to cool at all. The most likely cause is a defective compressor, although other parts should be checked before replacing this expensive component. An air conditioner compressor that won't start may have an open circuit when tested for continuity. Next, inspect the start capacitor, which helps cycle the compressor on. A bulging, leaking, or failed start capacitor can prevent the compressor from running. A defective contactor is another common cause because it sends line voltage to the outdoor condensing unit when it receives a low-voltage signal from the furnace control board. Less commonly, a failed run capacitor, capacitor, or dual run capacitor can keep the compressor from starting. Turn off power at the disconnect box and circuit breaker before inspecting components, and do not work on 240V wiring unless you are qualified. Capacitors can hold a dangerous charge. Compressor replacement or any repair involving refrigerant or the sealed system requires an EPA 608-certified HVAC technician. Enter your model number to find the exact replacement part for your central air conditioner.
01 - Central Air Conditioner Compressor
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.
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Highly Likely
02 - Central Air Conditioner Start Capacitor
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.
Common
03 - Central Air Conditioner Contactor
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.
Common
04 - Central Air Conditioner Run Capacitor
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.
Less Common
05 - Central Air Conditioner Capacitor
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.
Less Common
06 - Central Air Conditioner Dual Run Capacitor
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.
Less Common
Frequently Asked Questions
Why is my central AC compressor not running?
How do I troubleshoot an air conditioner compressor that won't start?
Can a bad start capacitor or run capacitor stop the AC compressor from running?
How can I tell if the AC contactor is preventing the compressor from running?
How do I find the correct replacement part for my central AC compressor problem?
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