Dometic 5 Button Thermostat Lost One Zone

Go to the Zone 1 control board and unplug the phone type modular plug. Look at the plug and see if it is corroded. The NORMAL wire flow on the phone type cable is----The tstat phone cable goes to the front AC (Zone 1). Then the Front AC has a phone type cable that goes direct to the rear AC (Zone 2). But the tstat Phone type cable CAN come from the Zone 2 control board. It is just most OEM's run it from Zone 1. IF you do NOT see Zone 1 but Zone 2 operates, it is possible that the tstat cable goes to Zone 2 first and then to Zone 1. IF the cable between Zone 1 and Zone 2 is corroded or cut/chewed, you will not see Zone 1 on the wall tstat. Are the roof units low profile Penguins? What year model is the RV? Doug