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jarwiebe · 09-23-2021, 11:40 AM

I am at a loss as to where to look for my air leak. Here are the symptoms:

With air bags dumped, parking brake applied and engine at 1,000 rpms my air compressor cycles, every 3.5 minutes (3 minutes unloaded, ½ minute loaded for a 14% duty cycle). Primary and secondary tanks hold steady pressure.

I put a gauge on the wet tank and I shut off the engine right after a dryer purge, the wet tank holds pressure (dropped from 130 to 95 overnight).

In the morning (with engine off) I aired up the wet tank with shop air. It purged at 130psi then dropped to 117 and holds there.

I have been unable to detect any leaks anywhere in my air systems using a water/soap spray.

My suspensions were the control air line for the VGT turbo. As far as I can tell, this is the only line that changes state (while compressor is in the unloaded state) from no pressure when engine is off to pressurized when engine is running. But I found no leaks on that line with engine running. I have not disconnected this line and plugged it to see if I have an internal leak in the air actuator on the turbo.

Your thoughts would be greatly appreciated.

96 Wideglide · 09-23-2021, 11:47 AM

What make air dryer?

jarwiebe · 09-23-2021, 12:16 PM

Wabco

jarwiebe · 09-23-2021, 04:18 PM

Quote:

Originally Posted by jarwiebe

. . . My suspensions were the control air line for the VGT turbo. As far as I can tell, this is the only line that changes state (while compressor is in the unloaded state) from no pressure when engine is off to pressurized when engine is running. But I found no leaks on that line with engine running. I have not disconnected this line and plugged it to see if I have an internal leak in the air actuator on the turbo.. . .

Ok, I just eliminated the air actuator on the turbo as a source of my leak. I disconnected and capped the line, ran the engine and it still cycled at 3.3 minutes.

Next step will be the unloader valve. I didn't have the right fittings so couldn't provide shop air to the unloader valve to test. Will make a run to NAPA tomorrow to get some fittings.

Tha_Rooster · 09-23-2021, 05:39 PM

I had a hole in a air bag making mine purge often.

jarwiebe · 09-23-2021, 06:30 PM

Quote:

Originally Posted by Tha_Rooster

I had a hole in a air bag making mine purge often.

I have eliminated the air bags by dumping the air. With air dumped I still have short cycling suggesting the bags are not the problem.

426smartin · 09-23-2021, 06:40 PM

Ray,IN · 09-23-2021, 06:52 PM

Wideglide gave you the answer. How long since you serviced the Wabco-Meritor air dryer? It should be serviced approx. every 3 years for occasional use, annually for full-time use. IMO the majority of compressed air system issues are the result of lack of maintenance for the air dryer.

Pages 11-12 are the Wabco-Meritor diagnostic charts.

96 Wideglide · 09-23-2021, 07:06 PM

I had an issue with my original Meritor Wabco system saver 1200 dryer.

It was randomly releasing low pressure tank air from the purge valve, long after engine shut down. I found it while I was under the coach, doing an oil change, and heard the air release.
I suspect an issue with the regeneration valve, but don't know for sure.

New dryer fixed my issue.

jarwiebe · 09-23-2021, 08:34 PM

My dyer was serviced 12,000 miles ago (6 years of short trips only). I pull my tank drain lanyards regularly and have never had and moisture/oil/mist expelled.

What has me puzzled is that my supply tank holds pressure when engine is off (been off for 5 hours now and has not lost more than 2 lbs) but losses pressure when engine is running. The only difference in these 2 scenarios is the compressor is running in the unloaded state.

Thanks for your feed back thus far, hope to test the dryer outlet check valve and unloader valves tomorrow.

jarwiebe · 09-27-2021, 03:31 PM

Got around to do some more checking. Took out the dryer discharge check valve and it was fine. Removed the air inlet line to the dryer and had no air feeding back.

Took apart the purge valve and it looked like new, reassembled and reinstalled.

I did a leak down test on the line from the governor to the compressor unloader valves. I disconnected this line at the governor and pressurized it to 120psi with shop air (engine was off). It had a steady loss of pressure of approx. 2psi per minute till it reached zero pressure. This line should not be losing any pressure. This would suggest unloader valves which has been my suspicion all along.

At this point my duty cycle of 17% is still within the allowable range of 30% so no immediate concerns but I'd like to get this resolved. I'll keep an eye on it but seek professional help when an convenient opportunity arises.

jarwiebe · 10-04-2021, 06:33 PM

Ok, two more items ticked of the "possible" list. I installed a new governor and air dryer (was past due for service by time). These items made no difference in my cycle times. I'm still leaning toward the air supply from governor to unloader. The line itself shows no leaks but it seems like I may have a leak of control line air in the compressor itself.