Bedroom Dometic A/C not triggering furnace to run.
I have 3 Dometic 630515.321 air conditioners, original equipment on my 2001 Affinity, and the bedroom unit will not trigger the diesel furnace to start. I have 2 zones for furnace (front and rear), and they both worked fine one night, and only the front zone worked the next night. As I understand the 3 temperature sensors in the coach go to each AC unit and the AC unit triggers the furnace to start. I have swapped zone 1 and 3 inputs on the furnace and the problem stayed with the rear AC unit, so I believe the furnace is fine. The fuses on all 3 units are fine. The thermostat recognizes the rear zone is calling for heat (the little underline appears), so that logic looks OK. I have the 5 button Duo Therm.
I ran the generator and the bedroom AC unit fan and heat pump work as expected. I checked and cleaned the phone cords, and swapped a new cord with no change. I also hot wired 12v to the 2 wires going into the relay board (12v is optional on all but the zone 1 unit), and still no help.
My guess is I need a new relay board. I could fix this one if anyone can help determine what component failed. The board looks fine.
Steve & Shellie
'01 Country Coach Affinity 42 #6012 Cat C12