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Old 07-17-2012, 10:30 PM   #1
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2000 27' Safari
Palo Alto , California
Join Date: Apr 2012
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Help - my Air Conditioner Compressor is Haunted

My 1999 Safari has a Dometic Duo-Therm Penguin Air Conditioner. Model number is 600315.321

The Air conditioner compressor seems to haunted. It has a mind of it's own and is ignoring the setting of the overall unit control - the compressor comes on by itself even if the overall unit is set to off. When I actually turn the unit on and set it to AC mode, it blows cold air just fine. I'm just worried it is going to break, blow up, catch on fire, or make blood start oozing out of the walls of my trailer.

On this unit, the controls (two dial switches) are mounted on the ceiling shroud. On the left side, there is a master control that has setting for fan only low medium and high, off, Heat and A/C low, medium and high. The right hand control is for temperature from warm to cool.

The compressor seems to obey the temperature control, but it ignores the overall unit control.

Where this becomes a problem is if it gets really hot in the trailer when we are gone for the day - the compressor will come on even if the unit is turned off, even if I set the temperature control to the warmest setting.

It took me a while to figure out I could isolate the problem by flipping the circuit breaker on the main panel for the Air Conditioner to off - I carry a Honda 2000i and that was overloading as soon as I plugged it into the trailer on hot days until I had an AHA moment and turned off the power to the Air Conditioner circuit at the main AC panel.

Anyone have an idea what could be causing this and whether it is fixable at a reasonable cost?

My guess is that the main control should be controlling a relay governing the compressor and that the relay is stuck closed so the compressor is always powered regardless of the main control setting.


- Dan

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Old 07-18-2012, 10:39 AM   #2
Rivet Master
1981 31' Excella II
New Market , Alabama
Join Date: Sep 2011
Posts: 5,280
You probably have a short that is shunting power to the compressor when everything should be off. The thermostat is out of the loop when the power is in the off position. I don't know if there is a master relay or not. I expect the power switch powers the thermostat and the compressor is cycled on and off by contacts in the thermostat. So the switch is in series with the thermostat. I would think you have a short that is powering the compressor independent of the switches. If there is a compressor relay it could be getting stuck. The points maybe welding together or there could be a short causing the relay to close when the power is off to everything else. You should be able to download a schematic from Dometic.

I had a relay weld to gether in a home unit one time.


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Old 07-18-2012, 11:50 AM   #3
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2008 25' Safari FB SE
Grand Junction , Colorado
Join Date: Sep 2007
Posts: 10,814
First thing I would do is clean all the electrical connections and clean out any dust or dead bugs—they can cause shorts. On a hot day, things expand and can cause a short. If a relay is welded together, it probably needs to be replaced though sometimes you can separate the contacts, it is probably fried.

A 2,000 w. generator is too small for most recent model A/C's and while the A/C may run, it probably will not get enough voltage to run properly. Check the plate on the A/C or the instructions to see how many watts it is rated at.

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