I'm thinking it all has to work at the same time to be good. I replaced the board and the thermistor, and it worked for a while. I too had erratic temps, similar to OP. I think I found a bad exhaust thermostat, that did not allow a fan to come on. I have owned this unit for three years and have never heard the fan come on. It is supposed to come on at 158 (condenser surface temp) and turn off at 133. I got a new thermostat, but then the calendar caught up with me, so I will see what happens next spring. I will try about any combination to keep from buying a new frig!