Question about Dometic Rooftop RV Air Conditioner

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Roof top AC unit on travel trailer hums as if trying to run even when turned off at thermostat. Eventually pops 30 amp main circuit breaker (not just A/C circuit breaker). I've turned the 20 amp A/C breaker off to stop the problem for now and wonder if anyone has an idea of what might be wrong.

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Hi, this sounds to me as though your compressor is locked up and what happens is it will overheat and before it can trip its own overload, it is drawing enough amperage to trip your 30 amp main breaker! If you are able to get up top and remove the cover on the unit, have a friend turn it on and see if you can see if its the black compressor humming, or the condenser fan motor which should also be up and running. If you can isolate which part it is such as that motor, or if it is the compressor which I am sure it is because it is the one part that would draw enough amperage with a locked rotor, ( L. R.A. ) to trip the 20 amp or 30 amp breaker. Do this check when the unit has set over night and the compressor will be cool to the touch. Now, when its first turned on if the compressor just hums at that time, you will have a locked rotor. We have what we call a hard start kit which is basicly a very strong start capacitor and relay that we install in series with your run capacitor that sometimes will break free a stuck compressor or a tight one. You should also look at your capacitor to see if it is swollen, leaking oil, burned terminals or any deformaty. It will look simular to a chrome soda can or a rectangular shaped chrome part that has wire terminals coming off the top. If it is a dual capacitor, it will have markings on the top such as a C- for common, Herm for hermetic compressor, F for the condenser fan motor on top. Try and locate this and look it over. If it is bad, this will cause both the fan and compressor to just set there and hum and over heat until the breaker trips. These are things you can check your self to narrow it down, but if it is the compressor, you will need a a/c repairman to do the repairs it needs. If you can see if the capacitor is in any of the conditions that I said earlier, make your self a drawing of it and mark how and color of wires attach to it and take it to a appliance repair retail store/ shop and they can check to see if it has the correct values like 5uf x 25 uf x 370 volts which ever it calls for. The cost for one is around $15. If this is the problem, it will be a quick fix for you and save you a bundle. Does the indoor blower put out air? If so thats good, the problem will be the run capacitor, compressor or condenser fan and hopefully not all 3!! Please don't forget to rate me on this and please keep me posted also. You may want to do the same with the thermostat if its not shutting off the unit. Take it in also if you think the run cap is faulty, but remember to write down the wire connections and it should be lettered such as R, G, Y, W. Please keep me posted.
Sincerely,
Shastalaker7
A/C, Heating, & Refrigeration Contractor

Posted on Aug 28, 2010

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Generic comments follow:

I'm not real clear on what you are asking ... I can almost guarantee you that you will not find a wiring diagram for your trailer.

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a

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