Forum Discussion

Impy's avatar
Impy
Explorer
Jun 24, 2016

Heat comes on, while running AC

I hunted around on the Internet and saw quite a few posts about the AC coming on when the heat was turned on in an RV. Mine is the opposite. I've got the AC cranking and suddenly I feel heat coming out by my feet. I have a Class C RV 1994 Tioga. The AC is a Coleman RV 7000 series and the furnace is a Hydro Flame Excalibur 8500-III. Originally, when I used the AC I made the newbie mistake of not realizing the thermostat was tied to the ceiling unit. I just turned on the ceiling unit and when I felt the hot air coming out - Iturned the thermostat down to off. My AC iced up - and I read up and realized that I needed the thermostat set. So I did and all is well - except the heat keeps turning on. It's easily 80+ outside, hot and humid. I turn the AC on and set the thermostat to 68/70 and I'll feel the heat kick on at some point. I turn the thermostat all the way down to get it to turn off but clearly I can't keep doing that. I pored through the manual and the only reference I could find to an off/on switch was a wiring diagram. I pulled the seat out and looked around for a switch. None. The AC has a circuit breaker but the furnace does not. How do I get the furnace to stay off?

The thermostat itself doesn't even look like the manual version. It's just a simple white rounded box. The top half has temp markings and a plastic stem that I pull up or push down (right or left) and the bottom half is the same except there is no stem - it reflects the actual temperature.

8 Replies

  • Impy's avatar
    Impy
    Explorer
    Jun 24, 2016
    Doug thanks for the link to the replacement. I can feel comfortable ordering it knowing what I know now.
  • Impy's avatar
    Impy
    Explorer
    Jun 24, 2016
    Thanks WNJJ and Almot. I feel confident that Doug nailed the issue. Like I said the manual and also trusted advice stated I needed the thermostat to keep the AC from freezing up. The fans are turned on by the tstat to help circulate air. But my thetmostat, is not the same as the manual.
  • Almot's avatar
    Almot
    Explorer III
    Jun 24, 2016
    In my rig the box like you described controls the furnace only :)
  • dougrainer's avatar
    dougrainer
    Nomad
    Jun 24, 2016
    Impy wrote:
    I am not the original owner. If I only knew then what I know now, only a month or two into ownership - what to look for....I'm assuming at some point all is not lost. That I could get someone who knows what they are doing to re-wire it. Thanks. I'll look for the 12v fuses and start pulling. It just kicked on again - and I had to lower the temp to get it off. It's now set at 40 - in the past I pushed it back up to 68/70 once I was sure the furnace was off. Now I'll turn it up and look for the naughty fuse and hope it only controls the heat.
    The Tstat is White-Rodgers. You are right - it does look like a run of the mill house tstat - back in the day...

    The EASIEST and low cost fix is to install the correct Coleman wall tstat. This link shows the wall tstat that was original. Doug

    http://old.rvcomfort.com/rvp/pdf_documents/1976190.pdf
  • wnjj's avatar
    wnjj
    Explorer II
    Jun 24, 2016
    It sounds to me like the t-stat is just for the heat and the A/C has its own controls. Without a heat/cool switch I don't see how it has anything to do with the A/C. Maybe what you read described a different t-stat that has since been replaced in your rig?

    If the A/C is icing up it may have other issues, possibly as simple as cleaning out the coils to improve airflow.
  • Impy's avatar
    Impy
    Explorer
    Jun 24, 2016
    I am not the original owner. If I only knew then what I know now, only a month or two into ownership - what to look for....I'm assuming at some point all is not lost. That I could get someone who knows what they are doing to re-wire it. Thanks. I'll look for the 12v fuses and start pulling. It just kicked on again - and I had to lower the temp to get it off. It's now set at 40 - in the past I pushed it back up to 68/70 once I was sure the furnace was off. Now I'll turn it up and look for the naughty fuse and hope it only controls the heat.
    The Tstat is White-Rodgers. You are right - it does look like a run of the mill house tstat - back in the day...
  • dougrainer's avatar
    dougrainer
    Nomad
    Jun 24, 2016
    This is what you posted.

    "The thermostat itself doesn't even look like the manual version. It's just a simple white rounded box. The top half has temp markings and a plastic stem that I pull up or push down (right or left) and the bottom half is the same except there is no stem - it reflects the actual temperature."

    That does NOT describe a RVP(Coleman) or any RV Tstat. It appears someone has changed out the original with a Home type tstat. If so, they probably miswired that tstat, which is a common problem when novices attempt to wire a home tstat to a RV. Are you the original owner of the RV? The Roof AC is indeed 120 volt breaker controlled. The FURNACE is 12 volt dc controlled. The Furnace 12 volt fuse will be located in the 12 volt fuse panel for the RV. If the fuse is NOT labeled, then have the furnace run and pull each fuse until it stops. Now, the bad news is this, Some RV's use the furnace 12 volt power to power the wall tstat and the controls for the roof AC unit. The roof AC unit, the controls are 12 volt powered. The 120 volt to the roof AC is just for the Fan motor and the compressor. Doug

    I should have mentioned. IF the wall tstat is a RVP(Coleman) it will state this on the tstat. Doug

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,367 PostsLatest Activity: Mar 10, 2026