Signs of HVAC Contactor Failure

If you suspect that a faulty contactor is causing problems, there are a few signs to check for to determine if this is true.

Continous Operation

When your heating system or air conditioning compressor fails to shut off unless you pull the plug or flip the breaker delivering power to it, this is a good sign of contactor issues. When the two metal pieces of the contactor become locked in place together the unit can't shut down even when the thermostat tells it to, according to G & S Mechanical Services. Blower fans and other interior parts of the system won't be forced to constantly run by a contactor, but rather a different electrical problem.

Failure to Start

The contactor closes and creates an electrical circuit to allow the HVAC unit to start after the thermostat calls for cooling or heating. When the contactor is damaged and needs replacement, it won't pull closed and connect the two ends even when you run a current directly to it, states HVAC Tech Support. If your thermostat is clicking on but the unit itself isn't starting, the contactor is likely dead or is not getting the electric current it needs.

Emergency Shut Off

Since a damaged or corroded contactor can cause the unit to run longer than it is designed to, the unit often shuts down to avoid overheating or blowing the motors. When pressing your heater or air conditioning reset button or switch allows it to turn back on, a bad contactor is likely the cause, according to HVAC For Beginners. Observing the unit to see if it is running until it trips the emergency shut off will help you troubleshoot the cause further.

Freezing Up

Frost development and accumulation on the inside of an air conditioning unit is another common indicator of contactor problems. Like with units that run constantly, the contactor becomes stuck in the on position and can't disengage. The air conditioner runs at top capacity for too long, dropping the internal temperature so low that condensation freezes inside, according to the Air Conditioning and Refrigeration Guide. Switching the unit off and letting it defrost should be done before you worry about replacing the contactor.