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Old 11-15-2011, 10:53 AM   #1
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1973 31' Sovereign
2007 20' Safari SE
Vintage Kin Owner
Wesley Chapel , Florida
Join Date: Oct 2011
Posts: 886
AC Thermostat failing?

The AC starts just fine when we turn it on.
Blowing Ice Cold.
Once the thermostat turns the ac off because it got the the set up temp it seems to work just fine...BUT!!!
Once is time for the AC to kick back on there is all kind of weird noises...The light dimmed out and it seems like there is a bad connection somewhere.
We tried to figured out what the issue can be and when it does it if we move the temp level to 60 it doesn't do is the thermostat failing?
Just wondering if the thermostat can be replaced with one of the digital ones of
Any advise?
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Old 11-15-2011, 06:48 PM   #2
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how is your trailer getting power? check the 120v voltage in the trailer. it might be a low voltage situation.

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Old 11-15-2011, 07:48 PM   #3
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1977 31' Excella 500
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I would never replace it with a digital one. Digital units require AA batteries to run them. With how seldom most of us get to use their trailers, you are guaranteeing a dead battery when you need A/C. I bought a new mechanical unit.

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Old 11-27-2011, 01:25 AM   #4
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Sounds like an internal check valve is leaking, and causing the compressor to start against a high pressure. Or it might be a bad capacitor in the start winding of the compressor motor. Any good auto air conditioner shop should be able to diagnose and repair, not necessarily an RV shop.
Let us know how it turns out.
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Old 11-27-2011, 06:53 AM   #5
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1969 27' Overlander
Albuquerque , New Mexico
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Veggie Bullet:
The thermostat is only a simple switch, so it closes ond opens a low voltage circuit that controls the AC unit.
Lights dimming, etc, mean the AC unit is pulling a LOT of electrical power (current). You'll need to have it looked at by someone who knows RV AC systems.
It might simply be time to replace the AC unit. If you have to replace the compressor, the cost of materials and labor, plus re-charge, could be close to what a new rooftop costs. (At least half)
Then, you still have a used AC unit!
I personally prefer electronic thermostats because they're way more accurate, programmable, and don't cycle on & off like the old mechanical units. Plus, what' a AA battery once or twice a year? You have to change the smoke detector batteries at least twice a year, anyway.
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Old 11-27-2011, 09:26 AM   #6
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I doubt it has anything to do with the thermostat as mentioned above that is only a single pole single through switch.

I am assuming you are waiting 5 or 10 minutes between cycles and the unit has a chance to equalize pressures. Starting a compressor within a short time after shut down will force ti to start against high head pressure.

The first things I would look at are the AC connections to the compressor and the connections in the electrical panel. Inspect for tight connections and any sign of burning at the connection indicating a loose connection. The unit starts off when at room temperature but once heated up any loose connection may begin to open thus increasing the resistance and dropping voltage causing chatter on start up.

Since the unit starts while cold I would not think it is the capacitor but if other thing check out it may require a look see.

You can prove the thermostat by just removing it and shorting the wires to starr the AC. Let it run for 5 minutes and the open the short. Let the things sit for 5 minutes and them short the wires. If the problem is there it is not the thermostat as you have bypassed it and provided a definite switch.
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Old 11-27-2011, 09:45 AM   #7
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I agree that an electronic thermostat is the way to go. Mine has an on/off switch and uses no battery power when turned off. Given the relatively few hours it is turned on in a year, the life of the batteries should approach shelf life. Mine has operated fine for 3 years on the original batteries and worked just fine again this morning when I turned it on for the first time this year.

John W. Irwin
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