Hi Gary - a few questions, and I have a RL, so the layout is a bit different.
Which unit has the thermostat that is labeled AC, Gas Heat, Electric heat ? Or does this unit have the option for heat pumps in both units ?
In my RL, the rear unit that serves the living area has the gas and electric and the front unit is AC only. Btw, I’m in Arizona also, but way up north in Page. As I write this it is 27 degrees outside and the coach is et to 68 and holding that temperature.
My front(bedroom) unit is shut off entirely. The rear ( main thermostat) is on Gas heat. If you set it to electric and outside temp goes below 40 degrees, the heat pump will gradually blow cold air. Sometimes the thermostat will automatically switch over to gas, but in my experience, it does not turn off the overhead unit which now blows cold.
If I know that temps are going below 40, I use gas only.
First thing to check is make sure the fan is on “auto” and thermostat that controls the furnace is set to “gas”. Other thermostat is “off”. A very common issue is that the vent hose in the bedroom area becomes unhooked from the register. If this happens, the basement will be very warm and also the bedroom floor will be nice and toasty under your feet. Feels great but not efficient ! Lol
Also, another issue is that depending on what wall the thermostat is mounted on, the inside of the wall can act as a very efficient carrier of air and screw up the temp sensor on the thermostat. Very common issue in the RL with the thermostat mounted on the wall by the steps, not sure where yours is.
In any case, unscrew the thermostat and stuff insulation and foam below the thermostat and into the wall cavity to insulate the thermostat from any airflow that can come up from the basement. If too much cold air is coming up this way, it would screw up the thermostat temp reading and it would think it needs to call for heat when in fact it doesn’t.
Hope this helps
Vaughan & Tracy 2013 RW 36RL, 2013 F350 DRW CC, 2016 Focus. MorRyde IS, MorRyde pinbox, disc brakes, Comfort Ride Hitch. "Life is to be embraced, Grab it with both arms ! "