[77newell]

Chester: you're a mensch (that's a Jewish compliment in case it's not clear). This stuff is confusing at times and we all (well at least me) are frequently confused. No need to apologize, we've all been there. It's great that clarity is coming to the problem through the interactions on with site. It's more important that your problem is being solved than exactly how and who helped solve it. None of us can know for sure what we are actually accomplishing, what we can believe in is the immense good will that exists on this site and that you have been both a giver and receiver of that good will. That is life as it should be.

[Richard]

This has been an interesting exercise. I am not sure it will help Chester, but it helped me to understand how the circuit works. It may help another guru in the future.

I am going to post two diagrams. I have copied the circuit board schematic from Page 5 of the installation manual. I enlarged it so my old eyes could see what was going on. I deleted the circuitry that allows the unit to run off an inverter to declutter the diagram.
I circled the relay triggers and the relays triggered to help the reader follow the electrical path, remembering that a triggered relay opens normally closed contacts, and closes normally open contacts. Relay 4 does not come into play for our purposes, it is associated with the inverter power setup.

   
 Notice on Low Cool, Relay 8 is activated, RL8 is Normally Closed, therefore any tstat signal to turn on Comp 2 will be interrupted by the now open RL8

   

And I posted this before I realized you had a handle on the issue. But it's all good, I have a spare board which may or may not be defective. I now know how to test it on the bench.

This has been great mental stimulation.

[Richard]

Well I'm glad we have some insight on the compressor issue. You may or may not know the systems came from SCS sealed with no ports for hooking up gauges. That's unfortunate. If you do have someone install test ports, do not allow them to use a "tap" port as the permanent port. They will leak. It's ok to use a tap port to evacuate the system, but install silver soldered ports before putting it all back together.

Still doesn't explain the sporadic behavior of the fans. Poor connection perhaps or a problematic relay.

Common is common, different legs of power all return to the grid on ONE common.

When you get ready to wire in the heavy duty relays, stick to the schematic you already drew.

[Chester Stone]

Well finally after many questions, answers, postings and testing, this issue is now resolved. Pulled the rear A/C unit, removed the side panels and made electrical tests and pressure test on the #1 compressor. Passed the electrical tests so proceeded to make a temporary addition of freon. Increased pressure held overnight so we then installed a permanent port to the front of the unit. I am lucky that compressor did not have to be replaced and not operates normally drawing about 8 amps. Thanks to all of you, especially Richard, for holding my hand. I have completed the installation of the heavy duty relays and will post under a new thread.