Definition
A contactor is an electrically operated switch in the outdoor unit of an air conditioner or heat pump that sends line voltage to the compressor and condenser fan. When the thermostat calls for cooling or heating, a 24-volt control signal energizes its coil and pulls the contacts closed; when the call ends, the contacts open and the unit stops.
Why it matters to you.
Pitted, burned or welded contacts can stop an outdoor unit from starting or keep it running after the thermostat is satisfied. Insects, leaves and cottonwood fluff that settle into Central Kentucky outdoor units can also interfere with the contacts.
Practical guidance.
If the outdoor unit keeps running with the thermostat off, or will not start when the thermostat calls, turn the system off at the thermostat and call for service. Contactor testing and replacement involve line voltage and are licensed technician work.
About this definition
Written by the Feistritzer Heating & Air Conditioning team — family owned and operated in Danville since 1976, Kentucky HVAC license M02584. Definitions inform; a whole-system diagnosis in your home decides.