Need help/info re furnace thermostat

[Lane]

Couldn't find this in a thread & could use help. I have a 2017 Airstream Interstate bought in April. A/C works great but just tried heat, & when choosing 'furnace' on digital thermostat and setting the temp, it begins by running the roof A/C and the floor furnace (propane) at the same time. After a few seconds I can turn off the A/C (click 'off' twice & the roof A/C will stop), but heat, which has gotten warm and working, finishes its cycle and stops about a minute after the A/C stops. Pretty self-defeating because the roof A/C puts out as much cold air as the furnace puts out warm air. I've never had a digital thermostat before, but how else would I turn it on other than clicking 'furnace'? ALL help appreciated! Headed to the mountains for Christmas and very worried.

[hbn7hj]

Look up the manual for the thermostat. If it is Dometic hold the mode and temp up buttons down together til two dashes appear on the display for reset.

They lose their minds sometimes.

[Lane]

Thanks.
Turns out we had the fan on 'low' and that was the problem. When we changed it to 'auto' it let the furnace take over without the A/C. Go figure.

[Doneworking]

Remember the "old tech" "Low Tech" mechanical thermostats? I am so old I remember mercury thermostats. Trouble was, they actually worked.

[booster]

Originally Posted by Doneworking

Remember the "old tech" "Low Tech" mechanical thermostats? I am so old I remember mercury thermostats. Trouble was, they actually worked.

We still have a Honeywell round mercury on sitting in the furnace room as an emergency one if needed. The auto setback learning units are really nice, but they do fail occasionally.


Mercury probably wouldn't work in an RV as they need to be level and momentum would also trip them

[GeorgeRa]

Originally Posted by Doneworking

Remember the "old tech" "Low Tech" mechanical thermostats? I am so old I remember mercury thermostats. Trouble was, they actually worked.

Originally Posted by booster

We still have a Honeywell round mercury on sitting in the furnace room as an emergency one if needed. The auto setback learning units are really nice, but they do fail occasionally.


Mercury probably wouldn't work in an RV as they need to be level and momentum would also trip them

I still have a chem lab mercury thermometer to precisely control bath temperature in the past. A tiny screw/wire can be magnetically moved to a setpoint position. I used it in my darkroom years. Mine is in the upper shelf in the garage but I found it online.

[mumkin]

Originally Posted by Lane

Thanks.
Turns out we had the fan on 'low' and that was the problem. When we changed it to 'auto' it let the furnace take over without the A/C. Go figure.

Sorry, but I missed your post as this is a VERY common problem - especially with the Dometic thermostat.

A very high number of new owners of Roadtreks come on our Facebook page because the AC unit fan has come on with the furnace the first time they turn it on. I had it happen with my 170 because it had been into La Mesa and the service guys messed with the settings. I wish I had a dollar for every time I have posted "put the fan on auto."