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Topic: Aux Compressor Intermittent Start (Read 769 times) previous topic - next topic

Aux Compressor Intermittent Start

Several weeks ago I posted that my aux compressor would not start if the head was pressurized.  I'm pretty sure that was a bad diagnosis.  The non-starting symptoms are repeatable with zero PSI. 

Once the pressure switch is calling for air, if I give it a firm bump or slap anywhere on the body of the motor or the compressor it starts.  I know next to nothing about electric motors.  I do know this unit has brushes and that they are a maintenance item.  Also suspect that a prior long-standing air leak caused this compressor to run a lot.

Ideas?
Mark Duckworth
2003 U320 4220
Build 6199, Motorcade 17971

Re: Aux Compressor Intermittent Start

Reply #1 –
Starting the compressor by hitting it could be caused by a sticking pressure switch. Test this by using temporary wires directly from the battery posts to the compressor motor (by pass the pressure switch).  My auxiliary compressor did not work when I purchased my U320 because the pressure switch orifice was plugged.
Wyatt
96 U320 40 WTFE, build 4943
84 Toyota Supra towd
2015 Jeep Wrangler towd
Victoria, BC, Canada

Re: Aux Compressor Intermittent Start

Reply #2 –
Quote from: P. Wyatt Sabourin –
Starting the compressor by hitting it could be caused by a sticking pressure switch. Test this by using temporary wires directly from the battery posts to the compressor motor (by pass the pressure switch).  My auxiliary compressor did not work when I purchased my U320 because the pressure switch orifice was plugged.
That's a great idea.  Will try this.
Mark Duckworth
2003 U320 4220
Build 6199, Motorcade 17971

Re: Aux Compressor Intermittent Start

Reply #3 –
Actually you can tap pretty hard on the pressure switch cover and if the compressor starts... you found the problem. The U shaped metal can be removed in order to clean the contacts or push down on the actual mechanism. No danger of a shock because it is all 12 volts. Cleaning the contacts may be necessary - try paper strips drawn through the cantacts as you hold them together by slight downward ressure. Pull paper strips through several times. Black on the strip indicates removal of debris. Good luck,

Jim
Jim Frerichs
2002 U320 42'

Re: Aux Compressor Intermittent Start

Reply #4 –
Finally got time to troubleshoot this issue and the pressure switch and solenoid are working fine.  The aux compressor has +12vdc and a solid ground on the power lugs (tight and clean).  A moderate thump on the casing of the aux comp motor gets it going every time. 
Mark Duckworth
2003 U320 4220
Build 6199, Motorcade 17971

Re: Aux Compressor Intermittent Start

Reply #5 –
Mike
Might be time to look at the brushes.
Sure sounds like worn or stuck brushes.
John Duld
1995 U320C SE 40'

Re: Aux Compressor Intermittent Start

Reply #6 –
Yup, could be worn brushes, flat worn out compressor, or just big voltage drop to a degree that starting is difficult.

I would pull you toad up close (battery side) to it and use jumper cables to the compressor.  The large gauge cables should give minimal voltage drop.  If pump now starts as it should, start looking at connections, both positive and ground and perhaps up-size wiring (up-sizing ground wire to chassis metal would be very easy.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Aux Compressor Intermittent Start

Reply #7 –
I have never heard my aux pump run, but coach stays level when parked for weeks/months at a time.  I suppose my question to the group would be how would I test the pump?  Create a leak by loosening an air bag line?

Thanks
Mike

Disregard...found it on beamalarm
Mike and Mari
'98  36 270 WTFE
Build #5272
Club #17504

Re: Aux Compressor Intermittent Start

Reply #8 –
Pulled the aux compressor out of the coach and removed the end plate to access the brushes.  Cleaned out a ton of residue, appears to be graphite / carbon powder.  Bearing felt good.  One of the two brushes was sticky, didn't slide back and forth like the other one.  Took some electronic cleaner spray and washed it out.  Moved freely after that.  Tomorrow I'll get it hooked up and see if this solves the intermittent starting.
Mark Duckworth
2003 U320 4220
Build 6199, Motorcade 17971