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My Dometic RV Rooftop AC Unit works Great when I have the A/C ON when I cut the A/C off the Freon pump motor is still activated and freezes the lines.

I have to cut the breaker for the A/C off completely I have diagnosed the issues down to the Relay Board, Thermostat, or Thermo Controller on the wall. Some pinpoint help would be much appreciated. I have found a new relay board online but do not want to purchase a part for it not to fix my problem.

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It could be that the contactor is stuck closed .The contactor is where the compressor wire goes to .There should be 2 low voltage wires (24 volt) that connected to either the side or top back of the contactor ,you can just pull 1 wire out ( shut power off unit first) then when power back on and compressor still run that mean the contactor is bad and needed to be replaced

Posted on May 17, 2017


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1 Answer

How do you add freon to a dometic rooftop a/c?

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If the Air comeing out is the same as the temp inside the RV make sure the compressor is running and not just the fans. It could be low on freon. If freon is ok then you would need to ck the wiring to the selector switch for a short. It would be obviouse because there will be melted wires. I am leaning toword low on freon since you have already been inside the wiring/control unit.

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You don't, they are a closed system, but if you can find an AC guy who is qualified, the can cut line & add valve, but can be expensive & no guarantee. Most find it's cheaper & better to replace upper unit if lack of freon is actual problem. What is unit doing that makes you think that's the cure?

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I recommend going with a new one. Both the coleman and the carrier are excellent and a whole lot more efficient that the 16 year old dometic.

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