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Old 12-01-2014, 08:24 AM   #1
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Air Compressor building air slower

When the air compressor fails, is it an open and shut case, or can it fail a little at a time? Mine has started to take longer to rebuild the air supply after going to ride height, or starting with tanks low, a lot of braking while parking. I have not yet been able to locate a leak that would be of the magnitude that would slow the rebuilding of the air. Are there any other devices that would allow the pressure to rebuild slowly. We have about 76k miles on the rig. I do have a couple of very small leaks that just barely bubble, but nothing of a larger nature. Thanks for your help or advise in advance. Happy Trails Bert
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Old 12-01-2014, 09:56 AM   #2
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About the only place I can think of where a leak of that size could hide is in the air dryer. Generally if the compressor has enough wear to slow the capacity there should be a lot of oil in the dryer and first air tank. It would be a creamy color and be somewhat thick and not smell good.
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Old 12-01-2014, 10:52 PM   #3
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The compressor draws it's air from the intake manifold, check the hose that connects them, have heard of the hose collapsing. The other problem, would be the compressor governor. I had to replace mine at about the same mileage that you have on your unit.
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Old 12-02-2014, 07:05 AM   #4
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Thanks both for your comments, going to do some more investigating today, also will replace the governor, thought of that right away, but assumed it was an on/off thing and would probably not make it build slowly. Will also check the air intake hose, if I can follow it up into the jungle. On the dryer, I will inspect the air dump closer for leaking, is there anything internal that can plug to cause a restriction? thanks again for your help. Have a great day. Happy Trails Bert
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Old 12-02-2014, 07:14 AM   #5
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I have found loose and cracked fittings, along with leaks in the pipes leading away from the compressor discharge. They only leak when the engine is running and very hard to hear. Check the pipes near any of the clamps that hold it, they sometimes chafe, creating a pin hole leak.


Also feel under the air dryer for a leak, while it is running and building pressure. If the unloader valve is gummed up, some air will leak out there.


Remember, until the first check valve in the system ( Air Dryer or Wet Tank ), the only time the compressor line will leak is when the engine is running.


In 40 years of fixing this stuff, I recall 3 compressor failures, 2 on Cat engines, where the drive spline stripped and one on a Mack truck that had a un-reported leak causing the compressor to cycle every 30 to 40 seconds. On that one, the air dryer was spitting out engine oil, from the compressor. By the time I got the repair, there was oil spitting out all of the air valves, including the parking brake dash switch. The driver wrote it up for oil on the cab floor.


One other place to check is where the compressor discharge line, first connects to the rest of the plumbing, sometimes there can be a build up of carbon blocking the first fitting. The compressed air is hot, coming out of the compressor and a little oil does cook on to the inside of the fitting.


I would not start throwing parts at this issue, until I was sure what's wrong.


Good Luck
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Old 12-02-2014, 07:18 AM   #6
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Besides the governor on the compressor, there is a "rotory" valve near/above the rear axle area on many coaches that sorts out the air pressure needs between the the reserve tank[s], and the air bags. This device can also be a source of leaks....
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Old 12-02-2014, 08:45 AM   #7
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Quote:
Originally Posted by Jobert View Post
When the air compressor fails, is it an open and shut case, or can it fail a little at a time? Mine has started to take longer to rebuild the air supply after going to ride height, or starting with tanks low, a lot of braking while parking. I have not yet been able to locate a leak that would be of the magnitude that would slow the rebuilding of the air. Are there any other devices that would allow the pressure to rebuild slowly. We have about 76k miles on the rig. I do have a couple of very small leaks that just barely bubble, but nothing of a larger nature. Thanks for your help or advise in advance. Happy Trails Bert
When was the last time you had the air dryer serviced?
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Old 12-02-2014, 08:24 PM   #8
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I'M BACK. Thanks so much for all the advise and suggestions. They all helped and the problem has hopefully been solved. I crawled under the coach today with it running and not in park (tires blocked well) with a squirt bottle and went after it. By accident while moving, I found the leak. It was a place where the hose was held in a clamp and had chaffed a hole through the steel wrap and there was a hole half the size of a pencil lead leaking. The old hose was very clean inside, which made things a little better. Replaced the hose tonight and will start it in the morning but all should be well. I also found that the air dryer had not been serviced as the dealer told me so will have to do that also. I had looked at it once and it looked like it had been changed, but had not. Thanks again to all for the suggestions, they were all good and I was starting down the list. You all are the greatest. Have a great day Happy Trails Bert
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Old 12-02-2014, 10:20 PM   #9
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Jobert, may I recommend buying the entire air dryer "kit" instead of only the desiccant dryer/filter. The associated valves in the air dryer body get gunked-up and should be rebuilt per air dryer maintenance schedule. I bought the filter only, changed it and discovered oil N water was clogging the spitter valve enough to leak air pressure.
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