Geothermal not keeping up.......77F right now.

This is the strangest thing.....

I killed power to the unit this morning to watch it start up. This time it called for stage 1 and used the A compressor (every other time it's been on the B side.)

Then when it went to stage 2 (lit y1 & y2), it started the B side.

Does it alternate stage 1 compressors? Or will it call the other side if the first does not respond?

 

So looking at the schematic......

Is it correct that all the following switches need to be closed for the compressor to run?

-High pressure switch
-low pressure switch
-low temp switch

EDIT: Never mind.....I test all of them. They're all less than .4 ohms on each side when the one side isn't working. So, it's none of those. Back downstairs I go.......

Thanks.

 

Abstract question.....

On my thermostat, it defaults to "O/B control changeover valve in Cooling" with "O/B controls....in Heating"

Is this correctly set?

 

Probably correct

If O/B were wired or configured backward, you'd get heating instead of cooling and conversely

 

I messed with it some more today.......The strange thing is:

If I shut the power down, disconnect the B-relay, the unit will fire back up on A-compressor (the problematic one.) Then, while it's running, if I plug the B-relay back it, it will energize and run the B-compressor along with A in two-stage. WTF?

I went through the schematic and double checked Y1 was wired to the correct board, then traced all the wires off of it. Did the same trace starting at Y2. Everything is where it's supposed to be.

 

This is getting progressively harder to diagnose with certainty from afar...need boots on the ground.

It is possible that operation of the 2nd compressor creates an interlock condition not present while just one compressor is operating, but that is a stretch.

 

UPDATE: It seems I had it all backwards. STAGE 1 is where the intermittent problem is. If I restart the system, the Y1 call lights comes on, and only the blower fan comes on.....the A compressor never starts. Then when Y2 lights, the fan goes to 100% and the B compressor starts. It's running in stage 2, with only the second compressor.

I can manually press the A-relay in and get compressor A to start, but as soon as I let go, it shuts off. If run leads from the B-relay and jump the A-relay, and it will close. So, it's not the relay--it's the power to the relay, or lack thereof.

One of the other things that I have found, if I do a cold restart with the stage 2 (B-relay) disconnected, the A-relay will sometimes close and start the problematic stage 1. Then if I wait until the Y2 call light comes on and reconnect the B-relay, all works normally. That's how I have gotten through the 108F days here in St. Louis.

Everything is working normally now, so I'm just trying to get as much info and ideas together so I can duplicate (if not explain) this to the tech next time.

Thanks again for all the support.