I have a 10 year of Rheem Criterion II that I use for Heat and AC. Now that we're using the AC we noticed this year that sometimes the AC unit turns on and then the fan continues to run with the engine starting up over and over again- even when the Thermostat is at the desired temp. We turn it off from the thermostat and it doesn't go off. I wiggled the wire from the thermostat to the Furnace and after 10 seconds it does finally go off.