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 and debris that settle into an outdoor unit over the damp Pacific Northwest off-season 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 Home Energy Group team — a family-owned HVAC company celebrating 25 years of comfort & care across SW Washington and the Portland metro, licensed in Washington (WA LIC# HOMEEGI003J7) and Oregon (OR CCB# 184255). Definitions inform; an on-site diagnosis decides.
