Dometic a/c always on

[ptylerp]

I have a Sierra 378 FB with two A/Cs controlled by Dometic thermostat. Last evening the Zone 1 A/C quit cycling on temperature control. No matter the temperature setting the unit comes on and stays on.

Zone 2 A/C works correctly and shuts off when desired temp is reached.

Zone 1 A/C starts shortly after the thermostat is set to cool and continues running even when desired temperature is reached. In furn mode the unit cycles on desired temperature and furnace operates properly.

I have did a "initialization" (thermostat off, select mode and zone buttons at same time) and it still does the same thing.

There is no error code and everything works correctly except controlling the A/C on desired temperature.

Any ideas?

[Platokidd]

do you have the fan set on auto ?

[ptylerp]

yes fan is set on auto.

[RiderBloke]

Is the Zone 1 unit actually blowing cold air? Try it without the Zone 2 unit and see if the temperature of the RV comes down. It does sound like the unit has lost its Freon.

[SilverArrowPro]

Auto means fans will always run, typically with 2 AC's they are ducted together, so your second AC will blow cold out to the middle ducts. Is the thermostat in the zone 1 area or zone 2? Typically one of the zones has a thermistor, and if that is blocked or went bad, it could cause the issue.

[ptylerp]

Each zone is controlled by separate temperature detectors. Zone 2 is in bedroom and zone 1 is kitchen/dining/living room area with the detector in the kitchen area.

With just zone 1 in cool mode and fan set to auto the room temperature was 76 degrees and thermostat was set for 79. The unit was cooling and just did not shutdown when the set temperature of 79 degrees was reached. At this same time zone 2 (bedroom) temperature was 73 degrees (only had zone 1 A/C operating.

Normal operation of this unit (zone 1 only) running will cool the bedroom quite cool before cooling the rest of the RV. To keep the temperature more even throughout the unit I will run the fan only in zone 2 and A/C running with fan in auto for zone 1. The fan in zone 2 will mix the cold air from the bedroom with the zone 1 air thus the whole of the RV has a fairly constant temperature.

Without a error code I just do not understand what is going on. The thermostat reads the actual temperature in the bedroom and the k/d/living room areas. Seems like a grimlin has entered the system.

If you have any other advice or suggestions for trouble shooting I would appreciate your ideas.

[litgrep]

Sounds like you've used the system for awhile and you've had it working. I don't know if the Dometic thermostat has a hard reset on it, but I'd look for one. Other than that, try taking all power off, both a.c. and dc for 10 to 20 min and reset every thing. If that doesn't work measure the thermostat control voltage to the a.c. units though the cycle and see what's not working. Good luck.

[ptylerp]

Not sure what changed but it is cycling by the thermostat as it should.

After initializing the thermostat it still did not cycle on selected temperature. Some time yesterday afternoon the A/C decided to play nice and cycle by the selected temperature on the thermostat.

Glad it is functioning properly.

Thanks for all the suggestions.

[litgrep]

Sounds like a loose connection somewhere. Check connections on the thermostat. Glad it's working now.