I have a ClimateMaster vertical 2-stage ground source heat pump. Closed loops, buffer tank, etc.

I started having problems with the system not keeping up on certain hot weather days, and the desuperheater was not providing any hot water. After checking the loop pressure, loop temps, refrigerant, etc., I finally realized that the second stage compressor was not kicking in [sometimes].

The call lights are lit for Y1 & Y2, but only the "B" compressor is running (blower fan is at full speed.)

If I manually engage the relay for the non-working [A] compressor, it fires right up, but will not stay on. And if I jump the A-relay, it works--not a bad relay.

So here's what really throws me......If I shut everything down, disconnect the relay for compressor B, and restart the system, the problematic side (A-side) fires right up. Then if I reconnect the B-relay (power still on), the B-side will energize and go into second stage along with A.

Y1 and Y2 are lit the whole time. The schematic confirms everything is wired correctly.

I have tested the high/low pressure & temp switches.....all are at .4 ohms.

I have a VisionPro IAQ running the whole thing, all the settings have been double checked. The only one I was unsure on was the default "O/B controls changeover valve in COOLING" vs. "...controls...HEATING."

I have had a tech out twice to look at this. Of course, both times second stage was working normally and it cost me $85. They don't seem to believe me when I tell them the second stage isn't working.

Any ideas would be greatly appreciated. I don't mind paying someone to fix it, but I need the damn thing to be broken when they get here! Or at least pinpoint what is acting up. Thank you so much in advance.