Im trying to troubleshoot a Climatemaster ground source geothermal. It is about 10 years old, and a 2 stage unit (2 x 1.5 ton).
When it calls for first stage, the fan and circulation pump runs, the compressor starts, runs for about 2 minutes, then the compressor drops out (everything else keeps running as long as there's a call for heat), and thus no heat on first stage. It waits a few minutes and trys again a couple more times before it lockout. When second stage kicks in, it works fine (the second compressor runs, fan speeds up, etc).
When I go into test mode on the control board, I get fault code 4 which is FP1 (water coil freeze protection). The limit setting jumper is clipped, for the closed loop/antifreeze system. I checked the gray wires going to the thermistor, and I get ~16k ohms (or more when running), which is about right by the manual (60*F). The compressor when it does run draws about 3.2 Amps which seems ok.
Any other things to check before I tell him to call a refrigeration person?