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Old 12-01-2022, 05:04 PM   #1
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Air system saga

I noticed the air gauges acting funny on the trip to AZ. However all worked ok other than I thought the gauge activity indicated an issue and the compressor was working OT. Took it in to a respectable truck/tire center and got the dryer filter changed and inspection. Tech says all is well, plenty of drum front and back. On the way home, the green gauge dropped rapidly, then returned to match red. Upon pulling into my site, the air crapped out completely. I am thinking governor but after seeing the installation, no way I am going to attempt to change it. Coach Net agreed to tow it back to the same place (I think the tech is solid and honest, also reasonably priced) so it's getting towed back. I insisted on a flat bed tow. My thinking is there was an issue and the new dryer shoved it downstream leaving either the governor or worst case the compressor is toast. I asked specifically if the air dryer indicated oil blow by, tech said no.
Thoughts ?
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Old 12-01-2022, 07:47 PM   #2
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Good decision, it's almost never the governor, they get changed because they are cheap.

Governor stops working, both gauges slowly go down together as you use air.

Compressor is before the dryer, the first thing in the system.

Leave it to the pro.
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Old 12-01-2022, 08:34 PM   #3
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If you have the VDC then cold solder joint at the sensor input
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Old 12-02-2022, 08:11 AM   #4
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Quote:
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Good decision, it's almost never the governor, they get changed because they are cheap.

Governor stops working, both gauges slowly go down together as you use air.

Compressor is before the dryer, the first thing in the system.

Leave it to the pro.
That is what happened, both went together - once I was stopped.
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Old 12-02-2022, 10:07 AM   #5
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so..update. This morning the coach aired up and the dryer purged. Then every 50 seconds the purge valve fired and the green needle dropped and aired up. So, I am thinking a purge valve aka "spinner" valve is bad. Will r&r and let y'all know if that works.
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Old 12-03-2022, 11:51 AM   #6
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so update to update. Installed a new purge valve successfully but the behavior is the same. The coach airs up to around 120 and the dryer purges, green needle drops 20 or so pounds (red doesn't move) and then it airs up again only to purge.
I feel ok to drive it in to avoid the trauma of a tow.

Any ideas ? I am back to thinking governor.
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Old 12-03-2022, 01:18 PM   #7
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I have a Cummins so went on line to the Cummins Quickserve site, lots of good info including symptoms lookup with trouble shooting guide. There were several listed under compressor and after reading it almost seems like it might be your compressor unloader valve.



Do you have access to the make/model of your compressor. Do some searches and you might be able to find info specific to your compressor.
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Old 12-03-2022, 01:25 PM   #8
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Thanks jacwjames, it's a cat C-7, cat compressor. Not sure of exact model, probably need the numbers off the motor. I hope the mechanic can figure it out, the fact the only the green line drops seems to be a hint.
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Old 12-03-2022, 01:36 PM   #9
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There is a check valve after the purge valve and air dryer, so no air from tanks can go back to them, but you found that out.

If the tank guage is dropping, you have a leak that you should hear.

If you continue to run like it is, first, the leak could get worse. Once air drops to low your parking brakes will apply, stopping you where ever you are.
Second, constant purging is causing your compressor to cycle to often. That over heats it, causes excess moisture and engine oil in the tanks.

Fix the leak.
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Old 12-03-2022, 01:40 PM   #10
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Quote:
Originally Posted by jacwjames View Post
I have a Cummins so went on line to the Cummins Quickserve site, lots of good info including symptoms lookup with trouble shooting guide. There were several listed under compressor and after reading it almost seems like it might be your compressor unloader valve.



Do you have access to the make/model of your compressor. Do some searches and you might be able to find info specific to your compressor.
Constant cycling without gauges dropping can be unloader valves. He has a dropping primary tank gauge.

Once the air gets into the primary and secondary tanks, it's passed thru at least 2 check valves, the main one at the wet tank and the double check from the wet tank to the 2 service tanks.
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Old 12-03-2022, 02:11 PM   #11
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any thoughts on the air dryer check valve ?
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Old 12-03-2022, 02:47 PM   #12
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Quote:
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There is a check valve after the purge valve and air dryer, so no air from tanks can go back to them, but you found that out.

If the tank guage is dropping, you have a leak that you should hear.

If you continue to run like it is, first, the leak could get worse. Once air drops to low your parking brakes will apply, stopping you where ever you are.
Second, constant purging is causing your compressor to cycle to often. That over heats it, causes excess moisture and engine oil in the tanks.

Fix the leak.
Coach is holding air. The purge cycle is regular and as mentioned only affecting the main. Like it's being told to purge, just too often. I agree that it's making the compressor work too hard. So, what tells the air dryer to purge ? Staring at the air gauge it doesn't appear to be over pressured prior to the purge and fills right back to the correct level.
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Old 12-03-2022, 03:34 PM   #13
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The air dryer purges every time the air compressor governor cycles as it reaches its set pressure (120). The purge itself is a shot of air from the purge valve on the bottom of the air dryer. It shouldn’t not continue to expel air other than the short burst. If the green needle on the gauge falls then air is leaving the system. When it reaches about 100 the governor will call to build the air back up to 120. The leak should be obvious if the gauge falls as quickly as you have noted. Soapy water in a spray bottle my help locate less noticeable leaks.

I would park the coach in a quiet spot, run the engine until it reaches 120 and you hear the air dryer purge. Shut off the motor and go to the air dryer. Is there any air coming out of the purge valve (hear a hiss or see bubbles). If there is, the valve needs to be rebuilt. If not, then look to see if the gauge is falling. If it is, there is a leak in the system somewhere else. If it is not falling, then use wheel chocks to secure the coach and release the parking brake. If the gauge is falling then your parking brake system has a leak. In this case it is usually the rubber diaphragm on the spring brake. Unless you are a very well versed mechanic, that repair should be left to a professional. The spring brake side is under extreme pressure and deadly if not handled properly. Good luck hunting this down.
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Old 12-03-2022, 03:47 PM   #14
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Thanks. It's raining to beat the band here in Queen Valley AZ. so I have an adult beverage, the Grateful Dead on and a steely gaze fixed on my air gauges sitting at 120 lbs. I replaced the purge valve today so I don't think it's a leak or the purge valve. Also I have a tri-tip resting on rock salt ready for the smoker. So in short, things could be worse.
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