I am going to dig into this more fully over the weekend including model numbers but for now, here is the dilemma.

My salon AC (three knob) works great in cooling mode. It is wired so that the water pump turns on and off with the compressor. When in cooling mode, both the water pump and compressor work fine. When running in heat mode over the weekend however, the unit suddenly stopped. On investigation I found the compressor humming and the water pump not on. I thought I fried the compressor but when I switched back to cooling, everything works great.

The question now is, what would cause the water pump and compressor to not run, only in heat mode. I'd say reversing valve but that would not affect the electric water pump, so it must be an extreme low voltage issue to both the pump and compressor?

Any ideas on where to look or test with the minimal information I have so far?