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Geocritter's avatar
Geocritter
Explorer
Jun 09, 2013

Roof-top AC acting oddly

I have a question about the original roof-top Dometic AC unit on my 1994 Holiday Rambler MH. It seems to be generally working okay, keeping the MH cool during the day (not an easy feat in Austin TX now that summertime is upon us). What has me concerned is that in the mornings, when it’s still fairly cool out, it sounds as if the AC compressor is turning on without the fan kicking in to move air through the unit. It sounds at first like a hum, then the hum gets louder as if the compressor is laboring harder, finally the unit will turn off with a sound like a very mild ka-thunk. It’ll remain quiet for 15-20 minutes and then start the cycle over again. Through all this the fan that blows air through the unit never goes on. Later in the morning, as the day heats up, the fan does go on and the AC general behaves normally. Does anyone out there have an idea what’s going on? Should I be concerned?

Thanks in advance for any help and insight y’all can give me.

Steve
Class A
  • Johno02's avatar
    Johno02
    Explorer
    Jun 10, 2013
    On 30A systems with two ACs, one is set to run on shore power, the other on generator. Look for a switch. Some have, some don't.
  • Johno02's avatar
    Johno02
    Explorer
    Jun 10, 2013
    If you are handy, changing the thermostat and control board is a DIY project. I used to be handy, now I am just a handful.
  • summerwinds48's avatar
    summerwinds48
    Explorer
    Jun 10, 2013
    Your bedroom A/C unit is probably hard wired to the generator A/C output. You might find a switch that selects between front/rear while running on generator A/C only. Try disconnecting from the external A/C, then try the front A/C unit on the generator to confirm if you have the same problem.
  • Geocritter's avatar
    Geocritter
    Explorer
    Jun 10, 2013
    It being a voltage drop in the morning doesn't make sense. It's only been in the 70's in the mornings and a lot of folks AC's aren't running. BTW I have a 30amp system and the site I'm on is set up to run either 30 or 50amps. I'm plugged into the 30amp outlet.

    Johno02, I've been wondering about the gagdity thermostat my RV has and have wished it were something simpler. Right now my bedroom AC only works off the generator (but that's a different story) the reason I brought it up is that I think a bad thermostat might be the problem with the bedroom AC.

    I purchased this old gurl very cheap, mainly because it's a rolling monument to what bad/no maintenance can do to a machine over time. I haven't had to spend a lot so far, mainly because whenever possible I'll repair things before I replace them.

    Steve
  • Johno02's avatar
    Johno02
    Explorer
    Jun 10, 2013
    I have the exact same problem. Service person checked and said that it is the thermostat and control board for it. He has ordered a new one is is going to install it asap. Apparently this is a common problem. Several service folks have told me the same thing. Mine was doing exactly what you describe, even with the thermostat set to OFF. We had to trip the circuit breaker to keep it off until we could get it checked.
  • doxiemom11's avatar
    doxiemom11
    Explorer II
    Jun 10, 2013
    That's what ours sounded like with voltage drop. We are 50 amp and were on 30 amp. AC ran fine except on the weekends when there were alot of other campers using the electric. When it was really hot, we had to use the generator until we got a voltage booster (couldn't leave - blocked in). We had no problems after we got the voltage booster.
  • crawford's avatar
    crawford
    Explorer
    Jun 10, 2013
    could it be a voltage drop everyone putting on coffee pots and toasters for breakfast time. Take a meter check what you have later when everything is working then check in morning.
  • Geocritter's avatar
    Geocritter
    Explorer
    Jun 10, 2013
    JackMS, probably a good idea, however the blower motor seems to be fine, it just doesn't seem to be kicking on when the compressor kicks on. During the afternoons, when it's 95 degrees outside, it works normally.

    Cuffs054, I believe it's an AC only, I'll check it out tomorrow when I'm back with it.

    Right now I'm sort of in limbo between moving out of my former residence (and getting rid of 40 years worth of "stuff") and moving into my RV home. Hopefully the move will be complete by the end of this week.

    Steve

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