Fixed an A/C problem (1703T)
 

On our last trip, the A/C cycled on and off (as it should) for half a day and then it stayed on permanently and we woke up freezing. Turning the thermostat knob though it's range produced healthy-sounding clicks as the switch inside did it's thing but the A/C kept right on cooling. :( With no electrical tools to investigate with, we had to turn the bloody A/C on and off manually . . human thermostats, so to speak.

On our return from the trip, I went inside a day or two later to investigate. Classically, the A/C was working perfectly, going on and off as it should when I twiddled the knob. Studying the A/C wiring schematic, it was obvious that the thermostat was the only item that could cause the problem of not shutting off, so I bought a replacement on eBay - they are surprisingly plentiful. So far, the A/C is working as it should. :D

I reason that the original contacts are worn or pitted such that, after working for some time, they would stick or weld closed and then stay closed even though the activating coil was de-energized. A common enough problem with mechanical contacts.

One caveat - which is why I'm posting:

The blade connectors on the replacement pointed down, not to the side like the original. Had I re-installed the metal cover on the underside of the thermostat housing, the wire connections would have certainly got grounded which is definitely not a good thing! ;)

Ted

Nice work, Ted! Excellent job of troubleshooting! Thanks for posting such a clear and complete description of the problem and what you did to correct it.

- Jack

Thanks, Jack!