Dometic Thermostat Issue

We're currently camping in a colder climate & this morning started the "Furnace" mode on the thermostat.  For the first time ever, when the furnace started, the roof AC unit also started. The furnace blew warm air as expected, but the roof air unit was blowing cold air.  I turned the thermostat off & waited a few minutes, but when I again cycled the thermostat to the Furnace mode, the same thing happened. 

Any suggestion as to the cause & what the solution might be?

Bruce Clerico
2013 2910T w/Dometic Thermostat (pic below)

Try setting your fan on "auto".

Thanks for the quick reply.  Setting the fan on "Auto" solved the problem.

Posting on the Forum works every time!!

There is a known issue with Dometic Thermostats that is related to the Circuit Board "Floating"   The problem is exposed by removing the Thermostat's Front Cover. The Circuit Board is probably loose on the mounting screws.   The unstable mounting is obvious - if it exists.  The board "squirms" when pressure is applied.  That movement is enough to create a misalignment between the Control Button and Circuit Board Sensor.

The Control Board Sensors can be operated directly with the cover off and the direct contact with the control usually eliminates the signal problem.   I used a glue gun to apply a spot of glue in each corner of the Circuit Board to eliminate the wobble effect.

The thermostat needs to be reset.

With the thermostat off

Press and hold pressed tne + button and then press and hold the ON/OFF button until you see two dash's on the LCD.
Release both buttons and then press the on/off button again.

This will reset the thermostat.  You will have to set the auto/hi/lo
and heat/cool temp settings again.