Contactor
Updated
The contactor is the heavy-duty electrical switch inside your outdoor unit that sends high-voltage power to the compressor and condenser fan when the thermostat calls for cooling. When the call ends, it opens and cuts the power.
Every start and stop draws a small arc across its contact points, and over the years those points pit and burn until the switch either will not close or will not let go. A contactor stuck closed keeps the outdoor unit running even when the thermostat is satisfied; one that fails open leaves the unit silent no matter what the thermostat asks for.
Common Questions
What does a contactor do?
The contactor is the switch between your thermostat and the outdoor unit's high-voltage parts. A small signal from the thermostat pulls the contactor closed, power flows to the compressor and fan, and the AC runs until the signal drops and the switch opens again.
What happens when a contactor sticks closed?
The outdoor unit keeps running after the thermostat stops calling, which over-cools the house and runs up the electric bill, and it keeps the compressor working with no break. If your outdoor unit will not shut off, cutting power at the disconnect and calling is the right move.
How do you know a contactor has failed?
A unit that never starts, never stops, or chatters loudly as it tries to engage. Those are the usual patterns. The contacts are visible once the panel is open, so pitted or welded points show up quickly during an AC repair diagnosis, and replacement is straightforward.
Related Terms
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