The part(s) or condition(s) listed below for the symptom Central Air Conditioner Condensing unit does not 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.
Central Air Conditioner Not Cooling? Central Air Conditioner Troubleshooting
Central Air Conditioner Noisy? Central Air Conditioner Troubleshooting
Central Air Conditioner Fan Motor Not Running? Central Air Conditioner Troubleshooting
Central Air Conditioner Not Running? Central Air Conditioner TroubleshootingCentral 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 replace the compressor.
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.
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.
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.
A dual run capacitor will power both the compressor and the condenser fan motor. If the capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the dual run capacitor has failed, inspect the capacitor. If the capacitor is unable to hold and release a charge or is bulging or leaking, replace it.
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 motor control board helps to maintain the desired motor speed of the blower. When the motor control board fails, the blower motor may not run at the correct speed or it may not run at all.
A relay is used to control various air conditioner components. If the relay is defective, the compressor, fan motor, or other components may not function.
The wall thermostat has contacts in it that control the furnace. If the contact fails it can result in the furnace & condenser unit to not run at all.
The central air condensing unit is energized with 240 volts of electricity. This electricity then flows through the disconnect box to the compressor and condenser fan motor. The disconnect box enables the air conditioning unit to be turned off outside. The disconnect boxes 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 supply 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. If the disconnect box fuses do not have continuity, replace the disconnect box.
The furnace or air handler needs to have power reaching it for the central air condensing unit to run. If the control board has an indicator light, confirm the light is illuminated which indicates power is reaching the unit. If there is no power to the furnace or air handler, check the home's furnace or air handler's circuit breaker or fuse. Confirm the power switch on the side of the furnace is turned on.
The run capacitor for the condenser fan motor and compressor might be at fault. If the run capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the run capacitor has failed, inspect the capacitor. If the run capacitor is bulging or leaking, replace it.
Control Board
A wire harness, a group of wires with the required connectors and plugs, is used to control and monitor various central air components. If a wire harness is damaged, one or more of the components may not run or may only run intermittently. A damaged wire harness will need to be replaced.
The capacitor for the condenser fan motor and compressor might be at fault. If the run capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the capacitor has failed, inspect the capacitor. If the capacitor 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.
The furnace control board sends 24 Volts 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 will not provide voltage to the condensing unit. To determine if the contactor is at fault, use a multimeter to check for 24 Volts at the low voltage side of the contactor. If 24 Volts is present but the compressor and condenser fan motor still won’t run, replace the contactor.
