On our rig, we have two A/C's, and there is a control box below each A/C that has a comm cable connection. The comm cable connects at the thermostat, goes to the zone 1 A/C, which on our rig is the one over the living room at the rear. From that box, a cable goes to the furnace and also a comm cable goes to the zone 2 A/C at the front of the rig over the bedroom. The boxes have a dip switch on the circuit board, and the zone 2 dip switch has one switch marked zone 2 that is switched on, all the others on that dip switch are switched to the off position. The A/C's are both Dometic and the thermostat is the CCC2 that works with the control boxes. This is what the control box looks like.
https://www.amazon.com/Dometic-33120...%2C1051&sr=8-4