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Condensing Unit Does Not Run

The part(s) or condition(s) listed below for the symptom 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.

Most Frequent Causes for Condensing unit does not run

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Cause 1Wall Thermostat

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.

Parts
Cause 2Incoming Power Problem

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.

Cause 3Run Capacitor

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.

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Cause 4Capacitor

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.

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Cause 5Contactor

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.

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