Yep, that's it. So if that shuts off the compressor when the coil freezes, the part it is wired to is probably some sort of low or high pressure limit switch...guessing low.

Good things to know, but doesn't get me any closer to solving my mystery.

Thanks funair

 

......

 

Okay, what about the lines running to and from the evaporator? Are they cold, hot or equal to the 80 degree output temperature?

 

Infrared thermometer says 70 degrees low side pipes, 130 high side. I also (maybe foolishly) tried heating the "chinese hat" portion of the expansion valve a bit with a heat gun and no effect.

 

That sounds like the condenser readings at the radiator.