Question about Dometic Rooftop RV Air Conditioner

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Dometic roof top AC unit compressor turns on even if T-stat is off. Only way to get the compressor from turning on is to turn the breaker off. Unhooked T-stat wires to see if issue was there but the compressor still kicks on when I turn the breaker back on. If I leave the auto t-stat on, the compressor will turn on for a bit with a loud hum until after a couple minutes or more it shuts off with a loud thud that will shake the RV. Then after a while it will do it again. Only let it happen twice before turning breaker off as I am sure it is damaging the compressor. When I came back to the unit later, I switched t-stat on and set temp so it would normally come on, turned the breaker back on and compressor and fan came on as normal. However, when I moved the T-stat all the way up, niether the fan or the compressor would shut off after about a half a minute.

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  • Dometic Master
  • 6,674 Answers

Sounds like you may have a couple of problems there. First, have you checked incoming voltage to make sure you are getting 100-120 VAC at the AC control board in ceiling? If that's ok, try removing/disconnecting Ac compressor wire at ceiling control box and see if compressor shuts off then. May be a capacitor for compressor going or shot, and possibly relay in control box sticking, or bad wiring to thermostat. Have you had any lightning in the area prior to all this happening?

Posted on Jan 28, 2013

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Posted on Jan 02, 2017

22yooper
  • 828 Answers

SOURCE: duo-therm by dometic ac rv unit

I suspect that you have a bad selector switch for the on, off, low fan, high fan operation. If the selector switch is put into the off position everything should stop completely.

Posted on May 31, 2008

22yooper
  • 828 Answers

SOURCE: Compressor starts and doesn't stop

Relay for the compressor may be stuck ( Contacts welded) both the fan and the compressor should operate at the same time. Have the relay(s) checked and possibly replaced.

Posted on May 31, 2008

  • 587 Answers

SOURCE: RV air conditioner. Compressor running, fan stops before cool

The fan motor is getting hot and going off on the internal overload in the motor.
This is caused by either a low voltage, a bad capacitor, or tight or dry bearings in the motor.
To check the bearings turn the power off to the unit, then spin the fan blade if it spins freely then the bearings are ok.
To check the capacitor you will need some kind of tester or you can buy a capacitor and replace it, that's what a lot of people do. They usually don't cost very much.
To check the voltage you will need a voltmeter and measure the volts at the unit.

Posted on Jun 09, 2009

  • 332 Answers

SOURCE: RV Rooftop AC Unit

Sounds to me like your fan is hitting something
Remove the cover and turn the fan by hand ( with the power off ! ) See what it is hitting

Posted on Mar 06, 2010

motor1258
  • 6674 Answers

SOURCE: I have my dometic Rooftop AC unit. The

The compressor coming on does make a slight "humming" sound which is normal. Is the unit cooling properly? Do you think it is louder than before?

Posted on May 09, 2010

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The more rare scenario is that the control wire between the t-stat and the contactor is shorting to a power source causing the relay to energize. Good Luck!

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