Rooftop Central AC and heat unit gets stuck on when heater is left on for a few hours in winter months. Only way to turn it off is to throw the breaker off then back on.
Specs:
Lennox
model # gcs10x-511-75-1p

Could this be a fan relay? Contactor relay?

Depends upon what is sticking. Contactor for the entire unit or relay for just the fan. The thermostat wires could also be causing a problem if they somehow got damaged.

AC turns off, so it must be a fan relay. It's only with the heat after it's been turned on for 4 hours or more. I was just in there replacing the condenser fan and things looked OK in that area. I didn't see any damaged wires anywhere. This problem was before I had gotten in there so I know it wasn't me that caused the problem. I'll order the fan relay and see if that does the trick. Thanks for the advice. :cool: