Hopefully, hopefully you don't have the problem I had.
A mouse got in the ceiling and ate the communication wire that runs from the front A/C to the thermostat and rear A/C.
I found this out while trouble shooting the wires up there. I pulled on the com wire and came up with the butt end of it.
Long story short, I had to replace a working unit with a new unit that had the controls on board.
2013 Voltage 3800, 2012 Chevy 3500 HD
2010 Yamaha V Star 950
2009 Yamaha Raider
Volunteering with Habitat for Humanity Caravanners