I am having problems with the fridge compartment getting warm because the unit doesn't go into defrost mode - but the problem is intermittent. I first noticed the evaporator fan wasn't running when it should, and there was frost on the cooling rods. If I manually defrosted the unit with a heat gun, everything was fine for a few days. The defrost heater and thermostat tested OK with a circuit tester, so I replaced the defrost timer.

Then the problem got worse. The defrost quit working entirely and the cooling assy iced over. In this frozen state the defrost thermostat tested open - which seemed to designate a failure. I thawed the unit out with a heat gun and everything works fine again. Could a failed thermostat work intermittently? I have ordered the part just in case.

Also, I also tested the cold control and it always tests "closed" electrically. However, I am assuming that is because by the time I disconnect it, it has warmed up.

Am I on the right track with the thermostat? Is there a better way to test the cold control or should I replace that also?

Edit: Unit is more than 10 yrs old