Air conditioners comes on every time the heater does!

[AM_Allan]

I have a new Montana Mountaineer 5th Wheel with about 20 total days of use on it. I thought I had tested everything for problems, so this is likely an issue that started sometime within those 20 days. Now, when the heater comes on, the air conditioner also runs regardless of the temp set on the Dometec Fan/Cool/Furnace type thermostat. I can run the heater with the AC circuit breaker off, but I'd really like to fix this. It's under warranty, but I'd like to avoid dragging it into the dealer if I could do it myself. Any ideas?

[Old-Biscuit]

AM Allan wrote:
I thank all the above for their helpful responses. Jetcare's suggestion of putting the fan on Auto did indeed fix the problem. I never would have thought of that. I thought the AC had its own internal fan and was not related to the furnace system. Cold air only comes out of the round ceiling vents.
To NinerBikes: I read all my owners manuals. Unfortunatly, the furnace manual was not included in the package. Neither was the "fireplace" manual which has its own mysteries! 🙂

The A/C Unit has it's own fan and so does the furnace.

FAN on thermostat is for the A/C Unit fan, and if not in AUTO it will run when furnace is turned on.

[AM_Allan]

Wow! Kudos to you Chris for putting all those together for us. I printed out the users guide.
Thanks again to all.
Problem solved.

[Chris_Bryant]

I have the users guide here, and the longer owners manual here, as well as service manuals on my service manual page.

[NinerBikes]

AM Allan wrote:
I thank all the above for their helpful responses. Jetcare's suggestion of putting the fan on Auto did indeed fix the problem. I never would have thought of that. I thought the AC had its own internal fan and was not related to the furnace system. Cold air only comes out of the round ceiling vents.
To NinerBikes: I read all my owners manuals. Unfortunatly, the furnace manual was not included in the package. Neither was the "fireplace" manual which has its own mysteries! 🙂

Google is your friend... PDF, print out and save.

You might also want to check your air conditioner, and see if there is a vent tab register, that can be slid back and forth, to divert air out of the AC directly, instead of just the round vents.

[AM_Allan]

I thank all the above for their helpful responses. Jetcare's suggestion of putting the fan on Auto did indeed fix the problem. I never would have thought of that. I thought the AC had its own internal fan and was not related to the furnace system. Cold air only comes out of the round ceiling vents.
To NinerBikes: I read all my owners manuals. Unfortunatly, the furnace manual was not included in the package. Neither was the "fireplace" manual which has its own mysteries! 🙂

[Chris_Bryant]

FWIW, that's a "feature", meant to help circulate the furnace heat.
I'm not sure when they decided it was a feature though- during design or during testing.

[NinerBikes]

Heater should be run in " AU" for AUto position only. AC should be run in High fan or Low fan position.

Or read your Dometic owners manual that came with your 5th wheel. Read all the owners manuals that came with it.

[NinerBikes]

Heater should be run in "Auto" position only. AC should be run in High fan or Low fan position.

Or read your Dometic owners manual that came with your 5th wheel. Read all the owners manuals that came with it.

[Old-Biscuit]

jplante4 wrote:
Sounds like the thermostat has the RC/RH jumper installed.

Typical RV wiring is RC & RH jumpered......only one RED +


AS stated by jetcare.....make sure FAN is in AUTO

[jetcare]

Put you thermostat in the FAN position. You will notice the fan speed will be in either the LOW or High position. Move it to the AUTO position. Then you can put the thermostat back in the furnace mode and the AC fan motor will not come on.

[jplante4]

Sounds like the thermostat has the RC/RH jumper installed.