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Old 02-02-2021, 10:08 AM   #1
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A/C Issues, compressor not starting

Hello all,

Was wondering if any of you have much experience in troubleshooting AC systems. I am working on a Coleman Fleetwood 2005 pop up trailer.

Heater, Fan and AC all on same 20 amp breaker. Outlet is located under where dining table is located. This outlet does have the T shaped plug. Currently Heater and fan both function. When you switch to AC mode, the fan speed goes down and you can smell a rubber / electrical burning smell while the compressor tries to cycle on and off ( it tries to turn on for a few seconds, then fan speed increases then decreases again as it repeats cycle). If the breaker is turned off, nothing on the unit functions.

The AC was working fine for the last two months and shore power was installed that is capable of handling 30 amps.

What I have tried:
The unit has 3 capacitors. One for AC start, one for AC run and one for heater and fan. Both the Start and Run capacitors had been recently changed within the last 3 months before we purchased the unit and they still look brand new. Odd thing is when I disconnect shore power and try to short them to release the charge, neither unit produces a spark. I replaced the start capacitor hoping that it was just bad and noticed it still will not discharge when shorted after disconnecting shore power. It's like they are not getting charged at all.

I did find a 20 amp fuse blown on the power converter and replaced it, but same issue. Checked fuse again and it is not blown, even changed to another new one, same issue.

I checked the compressor resistance from Common to Start and found it at .5 ohms. Common to Run was at .1 ohms. Run to Start was at .6 ohms from what I have been told should mean that the compressor is ok. The only thing that concerns me is I thought that the resistance from Common to Start should be much higher but I really don't know. I also checked if there was a short from Common, Start or Run to the outside of the unit (tube that comes off the side of it) and found no open circuit.

I checked the thermal switch on top of the compressor with it disconnected, and found it to be an open circuit ( no resistance). From what I understand, this is the way it is supposed to be.

Thinking that it is time to call an HVAC certified repair guy at this point as I am out of ideas unless any of you have some ideas or comments on what I have found so far.

Thanks all!!
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Old 02-03-2021, 11:40 PM   #2
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Sounds like the compressor motor is bad. Try taking the wire off the motor and see what happens.

If it doesn't kick out the breaker, you will have the answer.
Happy Glamping, Norman & Elna. 2008 Winnebago Adventurer 38J, W24, dozens of small thirsty ponies. Retired after 40 years wrenching on trucks! 2010 Ford Ranger toad with bicycles or KLR 650 in the back. Easy to spot an RVer, they always walk around with a screwdriver or wrench in one hand!
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Old 02-04-2021, 11:46 AM   #3
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The motor windings appear to have continuity so they are not burned out. If the motor is mechanically seized, when the power is applied it will pull full LRA or locked rotor amps, than the overload on top of the compressor will open to protect the system.
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Old 02-04-2021, 04:35 PM   #4
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The capacitors will not hold a charge. What happens as long as there connected the motor winding (a/c is off) is acting as a short between the capacitor. About the same as charging one and discharging it by shorting across the post with a screwdriver.
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Old 02-05-2021, 11:07 PM   #5
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Hi Pat, don't know if you got it fixed yet or not. The overload you tested should be closed or have continuity across it. if it is open it is either hot from compressor tripping, or bad. You should normally see a resistance higher on a start winding than the run due to smaller winding to start the compressor. The testing procedure you described is exactly how you should have tested. The only thing I can tell you is if you were doing the tests with a hot compressor the resistance values will look odd due to the hot windings of the motor. if you check it cold you will see more of a normal reading. like 1.8 for the start and .9 for the run then start to run test would be like 2.7 maybe give or take. The rule of thumb for testing winding insulation factor with the multimeter is start +run within 10% of actual start to common run to common readings. It sounds like the compressor may be locked up or not have proper voltage to it. need to check voltage on the compressor while it is trying to start. That should have a potential relay if it has a start cap and run cap. testing the caps is a must as well. you will need a meter that can test microfarads uF. it is the only proper way to test the caps. If the potential relay is bad it will not start the compressor as well.
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compressor, not starting

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