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Topic: Thompson 12 volt compressor won't come on (Read 491 times) previous topic - next topic

Thompson 12 volt compressor won't come on

Compressor was working a few days ago. Now it won't turn on. Attached are photos. There is a switch a PO installed next to the fuse. The switch is on and relay clicks when switch is turned on. Using a 12 volt test light I checked the relay,  I have power on both terminals. Then I checked the pressure switch it closed and the terminals are hot. Next I checked the 2 wires going into the motor the black one is hot at the post on back of the motor.  Are there other diagnostics I can do? Is the compressor toast?
Tom and Michelle 2004 U270 36WTFS

Re: Thompson 12 volt compressor won't come on

Reply #1 –
Also there is gauge at the compressor it shows 110# after I started the engine and built pressure. I'm not sure the engine should pressurize this.
Tom and Michelle 2004 U270 36WTFS

Re: Thompson 12 volt compressor won't come on

Reply #2 –
I realized I said it was a Thompson compressor. I know it is a Thomas 1/3 hp. I guess my simple question is, if I have 12volts going to the post on the motor and the motor doesn't start running that would indicate the motor is bad? I also checked the ground and it is good on the other post.
Tom and Michelle 2004 U270 36WTFS

Re: Thompson 12 volt compressor won't come on

Reply #3 –
Quote from: T and M Long –
...my simple question is, if I have 12 volts going to the post on the motor and the motor doesn't start running that would indicate the motor is bad? I also checked the ground and it is good on the other post.
My simple answer to that simple question would have to be "Yes".

If you wish to pursue the matter further, there are many suggestions online for ways to "test" a 12V motor.  One example below:

How to Check an Electric Motor: 12 Steps (with Pictures) - wikiHow

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Thompson 12 volt compressor won't come on

Reply #4 –
Thank you Chuck. It is what I needed was hoping for a reset button or the like. This coach has me some what overwhelmed at times. I can't seem to learn new skills at the rate needed to keep up. Story of my life.
Tom
Tom and Michelle 2004 U270 36WTFS

Re: Thompson 12 volt compressor won't come on

Reply #5 –
Quote from: T and M Long –
This coach has me somewhat overwhelmed at times.
I felt exactly the same way 8 years ago when we purchased our coach.  It was our very first RV of any type - we'd never even owned a pop-up camper before we bought our U280.  Buying a diesel pusher motorhome seemed like a terrifying proposition, but we were so warmly welcomed and encouraged by the experienced members of this great Forum that we decided to take the plunge.  We have never regretted our decision.

The learning curve is steep at first, but will eventually level off.  Keep plugging away, read all you can find in the Forum archives, and ask questions when you are stumped.  We'll try to help however we can.

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Thompson 12 volt compressor won't come on

Reply #6 –
Yes the forum is awesome.  Would be completely lost without it. Now I am only mostly lost. 
Tom
Tom and Michelle 2004 U270 36WTFS

Re: Thompson 12 volt compressor won't come on

Reply #7 –
Well I have been looking at my compressor most of the day. Called Foretravel to price a new one $2100 with my discount (that really hurt my feelings). So took the compressor out, took the pump end apart to see if I could see a problem. Did not see anything with my untrained eyes. Put it back together and installed back in coach. When I turned it on it came on and ran. I let it run about 20 seconds,turned it off, hooked the hoses back up. I  turned the switch back on, the solenoid clicked but the compressor would not run. I took the unit back out took it apart. I took the rings off the piston and looked at them seemed ok to my untrained eye put them back on. Then I put everything back together and reinstalled back in coach. I flipped the switch and it ran and built air. I adjusted the pressure switch to 80#. I bled the air pressure down to 60 # it kicked back on and went back up to 80# and cycled off. I have no idea what I did to "fix" it. I have no illusion that it won't cause me more issues. I am not sure if I should consider a rebuild kit or what.
Tom
Tom and Michelle 2004 U270 36WTFS

Re: Thompson 12 volt compressor won't come on

Reply #8 –
Quote from: T and M Long –
I have no idea what I did to "fix" it. I have no illusion that it won't cause me more issues. I am not sure if I should consider a rebuild kit or what.
Well, first of all CONGRATULATIONS!  Perseverance pays off.

There's a lot of info on the Forum about rebuilding or replacing the Thomas compressor.  Search "rebuild Thomas compressor" and order the results to see the most recent topics first.






1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Thompson 12 volt compressor won't come on

Reply #9 –
Quote from: T and M Long –
I have no idea what I did to "fix" it. I have no illusion that it won't cause me more issues. I am not sure if I should consider a rebuild kit or what.

Tom,

With this latest info you most likely have a bad spot in the commutator. When the motor stops and one of the brushes is setting in this bad spot it will have the same symptoms. You may be able to remove the end cap on the motor along with the brushes. Remove the rotor and clean the commutator ring with emery cloth. You can check the brush holder and springs while apart to make sure one of the brushes isn't sticking. One other way to test this theory is the next time it quits see if you an slightly turn the rotor with something where it is exposed in the end cap. Then retry it.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Thompson 12 volt compressor won't come on

Reply #10 –
Thanks Mike.      Hopefully I can get back to this tomorrow.  After I got it running again ,I have been testing the function of the compressor. I have noticed that the first 15 to 45 seconds after it cycles on that it sounds like it is under a heavy load and runs slower, then it speeds up and sounds normal until it cycles off. The motorcade club tech Ronnie said I should check voltage before and while it's running. I did check this after I got off the phone with him. At rest I'm  getting around 13.6 v ,while running I get about 11.9v. Doesn't tell me much but might be a clue to someone more knowledgeable. I will also check the things you told me as well.

Tom
Tom and Michelle 2004 U270 36WTFS