My uncle has an Intermatic PF1222T timer unit. It has dual timers with a freeze guard thermostat.

The freeze guard thermostat did not appear to work when temperatures were in the 30sF, and it can be set to turn on as high as 50F. I jumpered the terminals on the thermostat and the pump started, which seemed to indicate the thermostat was likely bad.

I pulled the thermostat, took it home and threw it in the freezer. I then put my multi tester on it and found the switch had closed. After letting it warm up, it opened. I could hear the switch open as it warmed up. Of course, I could not tell exactly what temperature it opened or closed.

From what I can see, the thermostat switches a relay that overrides the mechanical timer. If I jumper the thermostat, and it kicks in the relay- which should tell me the relay is OK- what in the world could be wrong? Could the thermostat somehow not be registering the correct temperature anymore?