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Old 09-07-2015, 07:28 PM   #1
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Air dryer purge relief valve

This is a long post but will make it as brief as possible.
I have a Cummins ISL 425 HP engine.
The air dryer purge relief valve was purging every 55 sec or so. I was told the air compressor governor was the most likely problem. Changed the governor. Did not stop.
Next I rebuilt the air dryer. No change.
Called Haldex they said to remove the line from the governor to the dryer and if it continued to spit air then the valves on the compressor were sticking. Changed the head on the compressor. No change.
Then tried another new governor. No Change.
I was also told there was probably a leak in the air system somewhere causing the compressor to cycle so odten. I isolated the wet tank from the other tank and plugged each line one at a time. Left the tanks overnight and did not lose any pressure.
I am at a loss as to where I should go from here other than the local Cummins folks.

Does anyone have enough Cummins diesel knowledge to direct me to a next step.
A C Lowe
2009 Tiffin Allegro Bus 40QXP
Powerglide Chassis
Cummins ISL 425

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Old 09-07-2015, 07:41 PM   #2
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The Haldex troubleshooting guide may prove useful. I noticed it suggests solutions you haven't mentioned.

2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member,FMCA."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert the Constitution. "Abraham Lincoln"
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Old 09-07-2015, 07:59 PM   #3
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Air dryer purge relief valve

I failed to mention that I removed the input and output lines from the air dryer and the governor still sent a signal to the air dryer to purge every 15 seconds.
Thanks for the Haldex trouble shooting guide. I will save the link for future reference.
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Old 09-07-2015, 08:26 PM   #4
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(1) If the governor is remote mounted, check the 1/4" line from the governor to the unloader valve on the head of the compressor.

If compressor mounted check gasket.

(2) Plug the line from the governor to air dryer, at the governor. Takes air dryer unloader out of system.

(3) does the wet tank hold pressure ? Put a gauge in the drain port.

(4) Check the "check valve" in wet tank, from air dryer line. Wet tank could be leaking back thru it. That drops pressure and tells governor to pump again.

Post outcome.
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Old 09-09-2015, 01:03 AM   #5
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Location: Apple Valley CA
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I vote for #4 A C.

Craig & Carolyn Roberts Apple Valley, CA
2006 Newmar 3910 KSDP 400 ISL Cummins Spartan Mountian Master Chassis
Toad: 2017 GMC Canyon 4X4 Crewcab
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Old 10-03-2015, 10:59 AM   #6
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Thank You Ray. This is just what I have been looking for on the air system. You done good!

Dan & Linda (Red), 1997 Discovery, Freightliner XC Retired USAF, Ham (N7VEP), Sewing Machine Mech.
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