Forum Discussion

mileshuff's avatar
mileshuff
Explorer
Sep 21, 2014

Dometic AC, Thermostat no power, where is 12v fuse?

Air conditioning stopped working on my last trip. LCD thermostat display is blank. It's not getting 12VDC. Thermostat has 3 wires going to control box thats mounted just above the filter grill.

In my trailers circuit box there is no 12V fuse for AC, only a breaker for 110V. I'm assuming that the air conditioner supplies the 12V for the controller and tstat and that there is a fuse somewhere.

Is fuse inside the grey control box thats mounted above the filter grill or perhaps up on the roof under the shroud somewhere?

TStat I have is similar to this one:

Dometic LCD Thermostat
  • Rooted's avatar
    Rooted
    Explorer
    Feb 18, 2024

    Did you ever find the solution? I have the same problem. 

    • QCMan's avatar
      QCMan
      Nomad III
      Feb 19, 2024

      After ten years the OP is probably gone like most former members.

      • Rooted's avatar
        Rooted
        Explorer
        Feb 19, 2024

        Didn’t even notice the timestamp, just the title of a similar problem ha. 

  • mileshuff's avatar
    mileshuff
    Explorer
    Sep 25, 2014
    Bobbo wrote:
    Not to berate the obvious, but you DO have your house battery connected, right? If you use the battery disconnect switch, you lose the 12v to the thermostat as well as most everything else.


    Yes, that would cause many other items to not function if running on battery. This is while fully hooked up, battery connected too.
  • Bobbo's avatar
    Bobbo
    Explorer II
    Sep 23, 2014
    Not to berate the obvious, but you DO have your house battery connected, right? If you use the battery disconnect switch, you lose the 12v to the thermostat as well as most everything else.
  • mileshuff's avatar
    mileshuff
    Explorer
    Sep 23, 2014
    Chris Bryant wrote:
    Normally, the 12 volt power for the A/C will feed from the furnace.


    Looked into that and you are correct. Pulled the furnace cover off and there is a 12V circuit breaker that feeds the tstat. Reset that but still no display on the tstat. I did not have shore power hooked up but I would think thats not needed unless I want A/C. Tomorrow I'll get my volt meter out and do some more checking.
  • dougrainer's avatar
    dougrainer
    Nomad
    Sep 21, 2014
    There IS a 12 volt fuse in the 12 volt fuse section of your RV for the roof AC. The Roof AC does NOT convert the 120 volts to 12 volts. The 12 volt power is one of the small gauge wires at the roof AC control box and the 3 wires going to the wall tstat supply the power to the wall tstat. Doug
  • time2roll's avatar
    time2roll
    Nomad
    Sep 21, 2014
    The 12v feed does come from the grey box up in the ceiling however there is no fuse up there afaik. Good to go up there and check 12v power though.

    I think the fuse will still be part of the stack near the converter. Just a likely to be a bad connection up near the grey box.

    Good luck.

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