A/C fans run when Furnace selected on Dometic thermostat.

[Bigreg]

I have a 2018 M-367 FLS. I select Furnace on the thermostat and the a/c fan runs also. I have two units, same results with both. Any help would be appreciated.

[travelin texans]

Set the fan switch on the thermostat to "auto" rather than "hi" or "low".

[NH_Bulldog]

Originally Posted by travelin texans

Set the fan switch on the thermostat to "auto" rather than "hi" or "low".

X2

T-stat needs to be on auto. At least the AC and furnace are not fighting each other, it just moves more air around.

[ASCTLC]

I'm fighting this now. The Fan Auto/Low/Hi isn't what's wrong in my case, it's that setting a schedule automatically activates "Auto" function.
So I set the schedule to:
HEAT
START: 9pm
STOP: 7am
TEMPERATURE: 55*

I have verified that the schedule still shows "HEAT" and never changed to "AUTO" so it's not the schedule, it's when it activates that it ignores the command for scheduled HEAT. The control panel properly shows the HVAC "OFF" when not between 9pm and 7am.

So when 9pm rolls around the schedule activates and if it's warmer than 57* still then the damned Air Conditioner starts!!

Are you sure you aren't fighting this instead of simply the AC blower coming on with the furnace?

That's some crappy functionality!! I set the schedule specifically for HEAT but it automatically activates as AUTO. For now I've turned off the Air Conditioning breaker but that's a work around to what should not be an issue.

I started a thread a number of days ago asking who has separated the HVAC from the In.Command panel onto a common programmable thermostat (as I've put into my last two campers) for the needed flexibility to program for Wake Up, Day time, Come Home, Night Time but haven't gotten any responses.

For now, I just found it's stupid easy to disconnect the furnace from the Air Conditioner for control with a separate thermostat. That solves my AC/Heat dilemma but I'm quite confident with a little more research and testing I can get that Dometic Duo-Therm AC off the In.Command dependency too.

For now I'm super busy preparing for early November elk hunting (2 weeks of boondocking) and reliably functioning heat is critical so that's where all my effort is focused until that's over.

I'll probably just update my previous post so it can help someone else who's not satisfied to put up with this.

[bobbecky]

It's not the schedule that is the problem, but the separate fan control that is set to anything other than AUTO. What happens is, when the furnace is called for heat, only the A/C fan runs, not the compressor, and is designed this way so you can more rapidly circulate heated air within the trailer. By manually setting the fan control to AUTO you will stop the fan operation when using the furnace. It would help knowing what thermostat you have. This issue is common with the Dometic CCCII thermostat, and may also do the same with other thermostats.