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Haerveu's avatar
Haerveu
Explorer
Jun 10, 2014

ac compressor cuts on and off

Hello all!
I just got back from vacation to come back to my RV during 105 temps with my across deciding it doesn't want to work. My wife is so thrilled!
I've got a dometic 579 brisk air roof top ac.
Before I left for vacation I've never had any types of issues with it. Now, I can it on (ac) and it works wonderfully, then out of nowwhere I can hear the compressor ( think that's what it is) shut off then it just blows warm air ( fan still works fine). If I turn it off or to fan for a few min then switch it back to ac I can hear the compressor come back on and it gets cold again. I Cleaned it from the inside , it was pretty dusty. I went up and took the shroud off, wasn't dirty at all but I noticed the compressor ( think that's what it was) was really hot to the touch.
Any suggestions? I've got a voltmeter but have no idea what to stick where to test for anything. Being how its going to be in the upper 100s I'd like to figure it out pretty quickly. Also, there is a bare copper wire that's just kind of hanging out on the inside of the ac where the power plugs into, not an electrical wire, not sure if it goes into anything or not, I'm guessing its the wire to .measure temps? No, vents aren't being obstructed or blowing on the thermostat.

13 Replies

  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Jun 11, 2014
    sch911 wrote:
    Chris Bryant wrote:
    That sensor is the thermostat- *not* a freeze sensor (yours is a mechanical controlled unit, and has no freeze sensor). It should just be in the return air flow- not in the fins.
    I know you said the unit looked clean, but you need to give both sets of coils a good cleaning

    Yes its a thermostat to keep the evaporator from freezing up. So it is a freeze sensor. That's what we call it in the auto industry...


    No, it's not a freeze sensor. You can see the dial for the thermostat in the picture.
  • marcsbigfoot20b's avatar
    marcsbigfoot20b
    Explorer
    Jun 11, 2014
    That tube is for the air temp thermostat.....as in keeping the cabin at the correct air temp as what you set it to. It measures the incoming air and when it senses at the setpoint it cycles the compressor off. When it senses the air about 4-5 degrees warmer, it cycles on.

    There is no freeze sensor on the analog units.

    I have a digital thermostat upgrade from Dometic that I have not installed yet, and it has an actual freeze sensor seperate from the air temp sensor on the thermostat assembly housing.
  • sch911's avatar
    sch911
    Explorer
    Jun 11, 2014
    Chris Bryant wrote:
    That sensor is the thermostat- *not* a freeze sensor (yours is a mechanical controlled unit, and has no freeze sensor). It should just be in the return air flow- not in the fins.
    I know you said the unit looked clean, but you need to give both sets of coils a good cleaning

    Yes its a thermostat to keep the evaporator from freezing up. So it is a freeze sensor. That's what we call it in the auto industry...
  • dougrainer's avatar
    dougrainer
    Nomad
    Jun 11, 2014
    Haerveu wrote:
    OK I see, I stick the metal clip at the end of the sensor into the metal fins. Could that be the entire reason? Would that cause the compressor on the outside to be really hot?


    Clipping the TEMP sensor to the fins will result in short cycling. See Chris's post. This is a problem with the Internet. People thinking they know how to fix appliances. Doug
  • dougrainer's avatar
    dougrainer
    Nomad
    Jun 11, 2014
    From your description, the compressor is BAD. That is the reason it gets so hot. The Thermal overload is probably kicking it out from excess amp draw. The ONLY way to check your unit is a Compressor amp draw. No other way to verify diagnosis. Doug
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Jun 11, 2014
    That sensor is the thermostat- *not* a freeze sensor (yours is a mechanical controlled unit, and has no freeze sensor). It should just be in the return air flow- not in the fins.
    I know you said the unit looked clean, but you need to give both sets of coils a good cleaning
  • Haerveu's avatar
    Haerveu
    Explorer
    Jun 10, 2014
    This one did well keeping it cool ( 36 footer) all last summer in temps above 105 all summer. Anyways, I put the metal clip in the fans and 2 he's later its still working well. Not too sure if its BC the temp has dropped outside a bit. How can i check the volts just to the compressor? Thanks so much guys, well see if its still working tomorrow.
  • fla-gypsy's avatar
    fla-gypsy
    Explorer
    Jun 10, 2014
    Compressors get hot when operating. You may also want to check the voltage coming into the camper. Low voltage can result in issues. You do know a single AC is not likely to keep an RV cool in temps of 105 degrees?
  • Haerveu's avatar
    Haerveu
    Explorer
    Jun 10, 2014
    OK I see, I stick the metal clip at the end of the sensor into the metal fins. Could that be the entire reason? Would that cause the compressor on the outside to be really hot?
  • Haerveu's avatar
    Haerveu
    Explorer
    Jun 10, 2014
    I have no idea what the fin of the evaporator is, more Google searching.

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