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Duo-therm A/C...roof unit to the Comfort Control thermostat…

I have a Mobile Scout...
I have a Mobile Scout with a Duo-Therm A/C. I recently had to replace the 4-wire telephone type cable from the roof unit to the Comfort Control thermostat. It looked like a rodent had chewed it in half. I took this to a shop for the installation of the cable. They removed the refrigerator to fish the cable down the wall. I got home and started the a/c unit. It seemed to be working fine. I went off to do something else, probably an hour or two and found it not running and the breaker was popped. When I reset the breaker, something did not sound right. It was as if the compressor was cycling on and off. It did not take long and the breaker popped again. The next time I turned it on, the breaker popped after 10 to 15 seconds. Any ideas?
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Answered in 34 minutes by:
6/28/2010
Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 14,646
Experience: RVDA/RVIA Master Certified Technician with many years experience.
Verified
Hi: Thank you for coming to Just Answer with your question. My name is XXXXX XXXXX perhaps I can assist you with this. The first thing is to check the available voltage at your source. You want to see something over 120 VAC if possible. These are rated at 95 degrees on the ambient temperature at the unit. For each 5 degrees that goes up add an additional amp to the load. This can pull almost 20 amps on a real hot day with the temperature on the roof at 130 or more. Check the breaker and be sure it is a 20 amp breaker. I have seen some that were wired on a 15 amp breaker. Sometimes the engineering isn't the best on some of these systems. I hope they installed the correct cable when they put that new one in. A phone cable won't work. The plugs are backward. If you don't have a Multimeter to check the voltage you can get one at most automotive or hardware stores, Walmart or Radio Shack for about $15 and they are easy to use. Get a digital readout version if they have one. Easier to use. Go HERE for a complete Service Manual on this A/C should you need to go further. It has a trouble shooting guide of things to check. Get back to me if you need more help and let me know what you found. R.J.
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Customer reply replied 8 years ago
I went so far as checking the voltage at the control box in the unit as it comes from the source. It is 123.9 volts. The breaker is 20 amps. I have had a guy here locally suggest that I install a new control box. What is the next thing you would try?
Checking to see how much voltage is coming to the receiver on the ceiling........the part with the lights and beeps. That was the part I was referring to. If you have 12+ VDC to that with a phone adapter on there like the manual shows then the module should be fine.
Let me know what you find. R.J.
Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 14,646
Experience: RVDA/RVIA Master Certified Technician with many years experience.
Verified
Randall and 87 other RV Specialists are ready to help you
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I am not sure you fully understand what I mean and that is the purpose for the manual. You have to have the proper incoming AC voltage which you did. You also have to have the proper outgoing voltage to the t-stat. We always start with the easiest to rule out and work to the other. Once you have that eliminated you can move on. If you read my original post I gave you reasons for the breaker tripping..........and hope you checked them.
That manual covers just about every possible problem this unit can have. The VOM meter shows you what you have or don't have. Pulling too much amperage can be caused by several things. One is a bad compressor............but you have to rule out the other things first. And you never have to accept any answer on this site you aren't satisfied with. I do try to provide the needed materials for you to do your own diagnosis and you are free to follow that up with more questions. Hopefully that makes some sense........R.J.
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Customer reply replied 8 years ago
The thermostat is working fine. Before the cable change, it did not even come on. All buttons and screen data seems to be good.

I believe the problem is in the a/c unit itself.
You may be correct.............but, I have to go by steps one by one........if you have a headache I don't want to do brain surgery without checking a few other things out first. The manual will give you the steps to check each phase of the operation. If you want to check out the compressor and see if that is bad then take the cap off the top and take the wires off after you mark them. Take an ohms reading between each set of the three terminals. The sum of two should just about equal the sum of the other two pairs. Take a reading between each terminal to a ground and see if you have any sign of a short. These are all things we usually get to in order. Hope that is a little clearer. Let me know what you find. Again..........all in that manual. It is the same one I use when I do this. R.J.
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