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HomeRepair HelpLennox Central A/C RepairLennox Central air conditioner compressor won't run Repair
Lennox Central air conditioner compressor won't run
When your Lennox central air conditioner compressor is not running, the system may blow warm air even though the indoor blower operates. The compressor is the pump that moves refrigerant through the evaporator and condenser coils, so a failed compressor can leave the air conditioner compressor unable to start. However, check the more common electrical causes first. A failed start capacitor is a common reason an AC compressor will not start, followed by a defective contactor that does not send power to the condensing unit. Less common causes include a faulty run capacitor, capacitor, or dual run capacitor. Bulging or leaking capacitors indicate failure, while a multimeter continuity test can help identify an open compressor circuit or defective contactor coil. Turn off power at the disconnect box and circuit breaker before inspecting parts, and remember that capacitors can retain a dangerous charge. Compressor testing and any 240V line-voltage work should be handled by a qualified technician. Refrigerant or sealed-system repairs require an EPA 608-certified HVAC technician. Enter your Lennox model number to find the exact replacement start capacitor, contactor, run capacitor, or compressor for your specific central air conditioner.
01 - Lennox 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 - Lennox 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 - Lennox 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 - Lennox 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 - Lennox 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 - Lennox 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 Lennox AC compressor not running?
How do I test a Lennox AC capacitor when the compressor won't start?
Could a bad contactor cause my AC compressor not to run?
How do I find the correct Lennox compressor or capacitor part for my AC?
How can I tell if the Lennox compressor itself is defective?
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