I have two Compressors and one air handler. The thermostat has two control arms that are linked together (move one control and the other moves). It appears that the second compressor only comes on during high demand times. I am not a HVAC person at all and have no idea how it works. I was just wanting upgrade the old manual thermostat with one that can be programmed.
That is interesting to know. Not something we can help you with in the forum other than to advise you to contact a qualified, licensed HVAC contractor for guidance. This is not a DIY forum.