Try this, reinitialize the thermostat: From Dometic-
A system initialization will need to be performed by the installer after
the system is installed.
• Make sure the Single Zone LCD thermostat is in the Off condi
See page 4, “Quick Reference To Control Buttons”.
• Press the “
+” button and, while holding it, also press and hold
the On/Off Mode button for three seconds. LCD will show
― ― .
Press the On/Off Mode button again to turn system off.
This completes the initialization.
Hope it works for you.