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Old 04-22-2013, 07:58 PM   #1
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Air compressor issue?

Just finished 1100 mi. trip in our '06 Travel Supreme 42DS04 w/ 400ISL Cummins. Had an issue with compressor not keeping up, like when using the service brakes lightly in a parking lot or traffic. On two occasions air got low enough to sound the buzzer..........the only way I found to get the air back was to stop and run the engine up to about 2000 rpm and watch the gauges. It also does this if the suspension is dumped - won't fill the bags at idle or even 14-1500 rpm fast idle. It has to be around 2000 to make the pressure rise. Wondering if it is a compressor issue or air governor, or maybe the air dryer? Coach has 45,000 miles, I'm the second owner............ JB

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Old 04-22-2013, 08:11 PM   #2
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The compressor itself is usually pretty trouble free. Since the governor is under $30 at most any truck shop and easy to change out, I would go with that plus service the air dryer. If the problem persists it may take a visit to the shop. I assume you have listened for the sound of a leak. Does it finally build up to cut off pressure? When fully aired up, if you cut the engine, can you hear air anywhere?

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Old 04-22-2013, 08:14 PM   #3
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Could be compressor but much more likely an air leak in dump valves, spitter valve on air dryer, tank bleed valve, parking brake actuator, etc.. Need to find a chassis shop w/good working knowledge of air systems on diesel rigs or your will be spinning your wheels w/a lot of semi pro help at pro prices.
Here is a full education in the process. Old Forester had an intermittent problem that only got real bad when it was cold.
Perspicacity & stick-to-itiveness found a solution, hopefully armed w/a decent air schematic you can track down the problem in a whole lot less steps & a much reduced wad of sweaty money. Your problem should be easier to pinpoint as it sounds way more pervasive.
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Old 04-22-2013, 08:26 PM   #4
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The coach will hold pressure for several days, never below 65 psi even after weeks in the barn. No audible leaks when fully aired up, and yes it will go to cutoff fairly quickly once it's revved up. Probably will service the dryer next and maybe look for that air governor - it's problematic enough that I've already dinged one front wheelwell liner with a brand new Michelin........ JB
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Old 04-23-2013, 04:50 AM   #5
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You could have a leak in the brake treadle valve, such that you lose air when applying the brakes. Or simple a broken air line to one of the brakes. Holding suspension air pressure is only one piece of the air system and the suspension air is intentionally isolated from the brake system air supply. Also, the air system will cut off the air supply to the suspension if the pressure drops to 65. That's to help retain air pressure to operate the brakes.

However, a clogged air dryer could give similar symptoms. If it hasn't been serviced in the last 18-24 months, I would replace that first, just to be sure.
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Old 04-23-2013, 05:38 AM   #6
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Just from looking at it, the air dryer filter is the OEM one, WABCO I think............... JB

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