As it gets colder, one of the common questions asked in forums is, “I turned my furnace on and the heat came on, but why did the air conditioner (A/C) also come on?” The shortest answer is, your fan in the air conditioner is turned on, you have to turn it to “auto” so that it doesn’t come on. For a Dometic Single-Zone Thermostat, here’s how.
- Press the On / Off Mode button until Fan is selected
- Press the + or – button so that the setting changes from “Hi” (High) or “Lo” (Low) to “Au” (Auto).
- Press the On / Off Mode button until Furnace is selected
In Dometic’s Words
For reference, here is the full Dometic Single-Zone Thermostat User Manual and this tidbit is on page #9:
Note: If additional indoor air circulation provided by the air conditioner is not desired during Furnace Mode of operation, select Au (AUTO) in the Fan Mode to shut the air conditioner fan off. If Lo (LOW) or Hi (HIGH) is selected the air conditioner fan will continue to operate on the selected speed.
Thank you that was a great help. I was ready to take it in. You saved me a long trip to the dealer. Thanks again.
THANKS was expecting it to be a costly problem to correct. THANKS again..
AC turns on when I turn furnace on.
It’s very likely in the thermostat. The steps I show should fix it.
Thanks for the info my fan was not set on auto.problem solved.
Glad it helped!
Thank you!! Thank you!!! Thank you!!! I read all the manuals and it said nothing about that.
Thank you that fixed it
Ur awesome.. I was getting worried
Thank you yes that worked…… What a relief!!!!
Thank you for the fix! My Coachmen (Forest River) owners manual didn’t cover this and a lot of things!
Please let me know if there are other topics that I can help with!
I was having the Same problem, I was up all night worrying about it… this worked.. thank you so much! Now for some sleep!
Thanks for the tip. Worked great for me.
Thankyou so much. Currently freezing my butt off in the trailer because I couldnt figure out how to run the heat without the ac on… thanks to this I fixed it. Bring on the heat
Thanks. This was driving me crazy.
Is it just the fan or is the AC compressor coming on?
Just the fan. I actually think the idea is to suck in warm air from the ceiling where the air intake is and then redistribute it using the ceiling duct work. Meaning, it’s by design to do this.
But most folks don’t like that it does it.
Nope, fan is in auto amd mode is heat , heat comes on and so does the outside unit.not a heat pump , also i am getting 22 v at C and Y …at C and W i am getting 24.7v … it should be a bad tstat..but when i jump off at board with tstat in off mode.Y to C , heat also comes on with out side unit.
May ne board and tstat because i am getting voltage coming back from tstat when i shouldnt. But when i take tstat out same responce.so when i pull the w wire.cooling comes on correct.if i pull Y wire heat comes on by itself.whats your thinking.andnits not j7st the fan the compressor is comming on.thanks .bp
One more Thank You. I also was going to take it in for service. Now it works just as it should. Thanks!
My ac comes on when the thermostat is on no matter which fan setting and with all zones in the off setting. I was hoping your recommendation would work but no such luck.
Do you have the same kind of thermostat as pictured?
It is a Dometic but a different model.
I have a 43ft hauler with 2 ac units so my thermostat has more functions for multiple xones.
Thank you so much, I was really getting frustrated and you saved our trip!
Great…..Worked 1st time. Froze my b— off last night….lol
Thanks For This INFO!
I’ve asked SEVERAL RV Dealers, and they had ZERO info on this!
Like others said with their makes manual, our Minnie heater manual also did not cover this . . .
gamgator2000 in Bishop, CA
Thank you! Found ourselves in this situation on our 2nd night of our new-to-us Work and Play. You saved our weekend!! It worked!!
Thank you for the tip save me a lot of time tearing everything apart
Thank you for that great easy tip.
Wow what a poor design. Thanks for the easy instructions, works great now!
Thank you so much for this! We shivered through the night for four days. I was prepared to go to the dealer tomorrow and tell them the air conditioner was defective. Your instructions were easy for me to understand and worked perfectly.
I wish I had thought to do an internet search from the campsite.
Thanks for the help.
Thanks for the kind words!
thanks I just had to set the thermostat to auto during heater mode.
Thank you so much. I was stymied by the digital thermostat in my 2019 camper. The thermostat in my 5th wheel definitely does not work that way. Your hint saved me a lot of time!
I’m new to RV! This was the greatest gift today! Learning that age 65 and divorced I can do it on my own, yes I can! Thank you so much!
Perfect instructions! It fixed the issue for me.
Omg! This worked! Thank you! My husband had been researching a solution. I used Google lens and hit on this post!