2015 FR REBH Fifthwheel with two Dometic AC units, One Dometic CCC2, one furnace.
Thermostat lost zone 2 (which is only for ac units).
1. Used reset, per the user guide, so CCC2 (thermostat) would find all available zones. And ohm checked the zone 2 sensor (it worked). Only zone 1 found
2. disconnected all (a/c and d/c) power for 30 minutes. Then repeated step 1. Still only zone 1 found.
(disconnected power for each of the follow steps).
3. replace circuit board on ac unit number 2 (bed room). repeated step one, only zone 1 found.
4. replaced circuit board in ac unit number 1 (living area). repeated step one, only found zone 1.
5. replaced thermostat, repeated step 1, still only finding zone 1.
6. bought a r11 25 foot (phone wire) connected between ac unit 1 and ac unit 2, by-passing the internally routed r11 comms wire. Repeated step 1, only found zone 1. HOWEVER, when I jumped the r11 cable, ac unit 2 began to run.
Restored air conditioning system to original configuration with the follow:
ac unit 1 has circuit board from ac unit 2
ac unit 2 has new circuit board
original internal r11 cable installed.
system only finds zone 1, system zone one works.
system will not find zone 2.