Question about Dometic Rooftop RV Air Conditioner

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The Dometic ac.heat pump is not providing cold air. What are the possible causes and fixes? It is about 6 years old.

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  • Mike Butler
    Mike Butler Aug 07, 2010

    Does the fan come on? Can you hear the compressor kick in? When the compressor kicks in, you should hear like a slight "Moan" and you may even see lights dim momentarily depending on what type of RV it's on, wiring etc. Is it a ducted system (cool air expels from ceiling vents throughout the RV.) Or is the air expelled from ceiling assy. itself?
    Is it tripping the breaker at all? Do you have a model number, as well as what type of thermostat on the wall?

  • ebbacke Aug 07, 2010

    The fan does come on. I don't think the compressor is coming on but would not bet on that. I probably need to get on the roof and remove the shroud and have someone turn the unit on. It is a ducted system. It is not tripping the breaker. The model number is 635016.321C . The thermostat is a comfort control by duo therm with 5 buttons to control all of the features. It had been running fine until we hit Tulsa and 105.

  • ebbacke Aug 07, 2010

    I just did a comparison between the front and the rear ac. It showed me that the rear, the one I asked about, compressor is NOT coming on. Could it be a bad capacitor?



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Could be possible, but normally when a capacitor goes, the compressor will try to kick in momentarily, then back out and when it does, it will draw a lot of current, and likely trip the breaker, or at least draw current down, and make lights in trailer dim momentarily as well. Can you hear a "click" (relay makes that sound) when you go from fan only, to cool on that AC unit ? It almost sounds like a faulty relay, if no current draw when switched to cool. I don't suppose you have a multimeter of any kind?

Posted on Aug 07, 2010

  • 6 more comments 
  • ebbacke Aug 07, 2010

    I do have a multimeter. There was no dimming of the lights as I turned on the ac. I would be most willing to check the relay if given a little guidance. Thanks for your reply.

  • Mike Butler
    Mike Butler Aug 07, 2010

    When you remove your ceiling assy, to clean filter, is there a metal control box there, with wires coming out of it, approx 6 " wide x 10" long, and also has your hydro cable going into it? I haven't had time to check the manual on your particular unit yet, but will soon, as some have the relays built in to that control box, and others have relays under cover on roof.

  • ebbacke Aug 07, 2010

    The unit is ducted into vents throughout the coach. The only filter(s) I clean are the little round ones at the intake spots. It must be under the shroud on the roof.

  • Mike Butler
    Mike Butler Aug 07, 2010

    Do you not have a filter behind grate at ceiling where return air goes in to ceiling assy.?

  • ebbacke Aug 07, 2010

    The unit is ducted into vents throughout the coach. The only filter(s) I clean are the little round ones at the intake spots. It must be under the shroud on the roof.

  • ebbacke Aug 08, 2010

    No large grate inside of coach. Both intake return vents and supply vents are 6"diameter vents throughout the coach. The relay must be accessible through actual ac unit on the top of the coach.

  • Mike Butler
    Mike Butler Aug 08, 2010

    I hate to ask more questions but, what type of RV is it that you have. I'm curious how the roof unit is held on. Normally there is a ceiling assembly on the interior that the upper roof unit is bolted to.

  • ebbacke Aug 08, 2010

    The ac units(2) are on top of a Newmar 38' Diesel Pusher. There are 16 round ducts in the ceiling about 6" in diameter, 8 on the supply side plenum and 8 on the return plenum. The plenums(2) run the length of the coach. The front air does supply ac to the plenum and throughout the coach as does the back air. The units must be bolted from the top to the supported opening in the roof. The back unit is not working, but the front unit is still working. They are ac/heat pump units.



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