[77newell]

From the diaphragm shown earlier in this thread it seems that the thermostat logic decides the number of compressors running and the CB provides ptotection against short cycling and maybe determining the fans that are running at any given time.

Under this configuration, if the circuit boards become unavailable but the system is otherwise functioning fine then it should be possible to substitute a small programmable logic control (PLC) for the circuit board. It wouldn't be as cheap as the board but would allow continued use of the system.