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HomeRepair HelpLennox Central A/C RepairLennox Central A/C Condensing unit does not run Repair
Lennox Central Air Conditioner Condensing unit does not run
If your Lennox central air conditioner condensing unit does not run, a bad run capacitor or a tripped circuit breaker or blown fuse is the most likely cause. A failed compressor is a possible but less common cause. The compressor pumps refrigerant through the condenser coil and evaporator coil, so a failed compressor can leave the AC condenser dead. A faulty condenser fan motor may show no electrical continuity, fail to receive power, or have seized bearings that prevent the fan blade from turning freely. If the condensing unit has power but the compressor and fan are both off, a sealed system problem, low refrigerant, or tripped low pressure switch may be responsible. A pressure switch can also fail, but replacing it requires refrigerant removal. You can inspect components and use a multimeter only if you are qualified to work around 240-volt line voltage. Refrigerant diagnosis, sealed-system repairs, pressure-switch replacement, and compressor replacement require an EPA 608-certified, licensed HVAC technician. Enter your Lennox model number to find the exact replacement compressor, thermostat, condenser fan motor, fan motor, or pressure switch for your central air conditioner.
01 - Lennox Central Air Conditioner Compressor
Central air conditioners use a compressor to pump refrigerant through the condenser coils located in the outside condensing unit and through the evaporator coils mounted on top of the furnace or air handler. While it's not a common problem, if the compressor fails, the condensing unit will not run. You can use a multimeter to test the compressor for electrical continuity, a continuous electrical path present in the component, to help determine if the compressor is faulty. If all other potentially defective components, such as the capacitor and condenser fan motor, are operating properly, then a qualified technician should ...
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Highly Likely
02 - Lennox Central Air Conditioner Wifi Thermostat
The WiFi thermostat has contacts in it that control the furnace. If the contact fails it can result in the furnace and the condensing unit to not run at all.
Common
03 - Lennox Central Air Conditioner Condenser Fan Motor
A faulty condenser fan motor can be responsible for the central air conditioner condensing unit not running. You can use a multimeter to test the fan motor for electrical continuity, a continuous electrical path present in the motor, to help determine if the motor is defective. You can also use the multimeter to determine if power is reaching the motor. You can also try rotating the fan blades by hand. If the blades do not turn freely, it's likely the motor bearings have seized and the fan motor will need to be replaced.
Common
04 - Lennox Central Air Conditioner Fan Motor
A faulty fan motor can be responsible for the central air conditioner condensing unit not running. You can use a multimeter to test the fan motor for electrical continuity, a continuous electrical path present in the motor, to help determine if the motor is defective. You can also use the multimeter to determine if power is reaching the motor. You can also try rotating the fan blades by hand. If the blades do not turn freely, it's likely the motor bearings have seized and the fan motor will need to be replaced.
Common
05 - Sealed system problem
If the condensing unit has power to it, the contactor checks out okay, but the fan and compressor are not running, it is likely that the unit is low on refrigerant which will cause the low limit pressure switch to trip and keep the unit from running. Since diagnosing and repairing a sealed system takes specialized tools and knowledge, a qualified service technician should diagnosis and repair the unit.
Common
06 - Lennox Central Air Conditioner Pressure Switch
A pressure switch is a safety device used to help prevent component and system failures. There are basically three types of pressure switches used in central air conditioning and heat pump applications: High Limit, Low Limit, and Ambient Temperature. Depending on the model, you may have one or more of these or none. The pressure switch(es) can be checked with a multimeter, referencing the wiring diagram for the circuit locations. Note: If a pressure switch needs to be replaced the refrigerant will need to be removed, requiring a qualified technician.
Less Common
Frequently Asked Questions
Why is my Lennox central air conditioner condensing unit not turning on?
What should I check when the outdoor AC unit is not running but the thermostat is on?
Can a failed condenser fan motor cause the AC condensing unit not to start?
What does it mean if my AC condenser has power but the fan and compressor will not run?
How do I find the correct Lennox AC replacement part for my model?
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