A/C & Heat Control

[d-mac1]

Thought I had a thermostat problem, got a new one, same problem.

Problem is, when I turn on the heat, the A/C fan kicks on too. Yes, I can switch off A/C fan via the breaker, but would rather have it working right.

Is the problem the control board that is under the A/C? Its Dometic part 3313191.000. Looks easy enough to swap out if thats the problem. Seems like thats gotta be it, but odd cuz its under the A/C, but lotsa wires go to it, so I'm guessing its connected to the furnace too.

Thanks!

[DarkSkySeeker]

>> The D settings have NOTHING to do with

Good to know.

[dougrainer]

DarkSkySeeker wrote:
I had perhaps the same problem (perhaps not).

My AC and furnace would run at the same time. Turns out my thermostat had a "differential" setting. D1/D2/D3. It was defaulted to D1. When set to D3 the problem went away.

I supposed it was that the thermostat was no longer looking for set temperatures so close to the actual temperature that it thought the RV needed heat and cooling.

I forget exactly how I change to D3. Something like pressing "up temp" and power at the same time.

See https://www.forestriverinc.com/brochures/0000/0000ThermostatSingleDometicManual.pdf

The D settings have NOTHING to do with the AC fan On or OFF in furnace mode or any other mode. Doug


In the FURNACE mode the system will cycle the RV’s furnace On
and Off based on the room air temperature and the temperature
set-point on the Single Zone LCD thermostat. The system can be
configured to operate using an On/Off differential of either 1 degree
F or 2 degree F. This feature is programmed during the system initialization. See “System Initialization” on page 3.
To set the temperature differential the system must be Off. Press
the “?” button and, while holding it, also press and hold the On/Off
Mode button for three seconds. Release the On/Off Mode button.
Then release the “?” button. Press the “+” button to toggle between
“d1” and “d2”, “d1” for 1 degree F differential and “d2” for 2 degrees F differential.

[d-mac1]

dougrainer wrote:

MFL wrote:
When plugged into shore power, the AC fan will come on with furnace, if the fan setting is to low, or high. If set on auto, then only furnace fan comes on.

Jerry

Correct. The OP could have saved money if he had just READ the Instructions for the AC system;) Doug

Page 8

https://www.intechtrailers.com/images/info/PDF/Dometic/operation-manual.pdf

Appreciate ya attaching the instructions...now I have em. Looked through everything they gave me....zero instructions on thermostat. Was trying to find original thermostat connection instructions cuz none came with the new one and its slightly different. I figured that out...as said, its not the thermostat.

The good news is, you guys saved me from buying a new controller...and I fixed the loose wire, so now we're cool :C and alls is well that ends well!

[d-mac1]

MFL wrote:
When plugged into shore power, the AC fan will come on with furnace, if the fan setting is to low, or high. If set on auto, then only furnace fan comes on.

Jerry

Thanks! So simple, I feel pretty smart! LOL

I'm guessing the other problem led to this issue, that being, a black wire that connects to one of the 4 bundles under the controller box vibrated loose (no A/C) and thus connection between thermostat and controller went AWOL (error code A1) (fixed that this AM), and maybe thats what caused the thermostat to revert to low....or someone pushed the button by accident to switch off auto trying to get something to turn on...dunno! In 9 years, never had the A/C fan come on with furnace.

[DarkSkySeeker]

I had perhaps the same problem (perhaps not).

My AC and furnace would run at the same time. Turns out my thermostat had a "differential" setting. D1/D2/D3. It was defaulted to D1. When set to D3 the problem went away.

I supposed it was that the thermostat was no longer looking for set temperatures so close to the actual temperature that it thought the RV needed heat and cooling.

I forget exactly how I change to D3. Something like pressing "up temp" and power at the same time.

See https://www.forestriverinc.com/brochures/0000/0000ThermostatSingleDometicManual.pdf

[dougrainer]

MFL wrote:
When plugged into shore power, the AC fan will come on with furnace, if the fan setting is to low, or high. If set on auto, then only furnace fan comes on.

Jerry

Correct. The OP could have saved money if he had just READ the Instructions for the AC system;) Doug

Page 8

https://www.intechtrailers.com/images/info/PDF/Dometic/operation-manual.pdf

[MFL]

When plugged into shore power, the AC fan will come on with furnace, if the fan setting is to low, or high. If set on auto, then only furnace fan comes on.

Jerry