Question about Dometic Rooftop RV Air Conditioner

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Coleman rooftop a/c unit is fried? i plugged my

Coleman rooftop a/c unit is fried? i plugged my camper trailer into a 240volt generator plug, and now the frig, ac, and radio won't work.. help!

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  • jj2walsh Jun 30, 2009


    I have checked the ac control box out and it seemed okay, Its a coleman roof top with wall thermostat, fuse inside t stat was good, i haven't checked for 12v yet...not sure how. the frig is a norcold, I took the cover off the back left sode of the control box, and there was a 3 amp fuse that was okay, but i didn't get the rest of it off, the part with the wires connected to it, i'm guessing there is another fuse in there? anyway thanks for response it was helpful. By the way, I have checked the frig plug for power and the breakers for the ac and frig.

    Thanks, Jeff



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If there Air Conditioner is wall thermostat controlled, then take the front cover off the thermostat and check the fuse. If the fuse is ok, then take the inside cover of the AC down and pull down the control box that is mounted in the intake section of the AC. It is held on with two wing nuts. Remove the cover and observe the relays and the incoming AC wiring. Make sure that none of this is burnt. If all looks ok, turn power on and turn the thermostat to High Cool and check if you can hear the relay click inside the control unit. If not, then check to see if the thermostat has 12V going to it. Start there and see how that goes.

If it is controlled by the ceiling mount t-stat and selector switch. Remove the inner shroud and check the incoming AC wires for OK. If they look ok then check the selector switch and the thermostat.

The Refer has protection from this. Depending on which refer you have (Dometic or Norcold), the process is a tad different. If it is a dometic, go to the outside of the coach and remove the access panel on the rear of the refer. Remove the black cover from the control board (lower left side) and check to make sure that the 120V fuse is good (You will need an ohmmeter to check). If it is fine the check to see if you have power going into the 12V block at the very bottom, rear of the refer. If there is 12V there, then check the plug that the Refer is plugged into for 120V. If none, check the GFCI circuit in either the bathroom of the kitchen. If tripped you will have no power to fridge. Start there and then we will move forward.

Basic same checks for a norcold, board is harder to remove as you have remove wires. Mark and remember where they go.

Hope this helps,


Posted on Jun 30, 2009

  • Jeff Myers Jun 30, 2009

    Your Air Conditioner and your refrigerator will not work without 12V. Even though they are 120V Appliances. The AC thermostat and control box are run off of 12V. Pull the front cover off of the tstat and look for the red and white wires. White is ground and red is 12V positive. Check to make sure that you have power there. If so, turn on the tstat to high cool and check for 12V at the control box on the yellow wire, that is the cool feed for the control unit. If all this is ok then I would say that your control box is bad.

    Check the refrigerator for 12V as well. Are the lights on the front of the refer working? What does it do on Gas mode?

    Good luck and keep me informed.



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I think you sre screwed. Sorry.

Posted on Jun 29, 2009


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