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Old 10-02-2014, 12:48 PM   #1
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Air system on coach

I've noticed when driving my coach, the air system seems to recharge or turn on the compressor to fill the tanks every minute and a half to two minutes. Is this time frame normal or excessive. I only noticed it because I was driving with the window open and I heard the loud air discharge (ejectors) and then soon after heard it again. I started watching the air gauges and that's when I noticed they would air back up every minute and a half or so. If I park the coach and leave it running my air does not go down. If I turn the parking brake off while in neutral while running the engine, that air does not go down either. It doesn't seem like I have an air leak because of the last two statements and I've walked around the coach and here no air leaking. When I level the coach and store it, it will hold air for at least a week and a half to two weeks which is in limitations as for Freightliner...

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Jason


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Old 10-02-2014, 01:11 PM   #2
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This seems excessive to me. I hear the purge while driving, but have never seen my gage move. The parking brake pads are engaged with springs. While traveling down the road, the system uses air pressure to compress the springs. In all of the scenarios you describe for identifying there is no air leak, there's no air to the parking brake. It could be possible you have a bad seal in a parking brake release diaphragm. Find a flat spot and block the wheels. With the engine off, disengage the park brake and see if you hear a leak then.
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Old 10-02-2014, 02:53 PM   #3
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That is why I released the parking brake with the coach running, to see if I was losing air from the brakes but gauge never moves and no discharge. Only while traveling down the road, does the air compressor kick in every minute and a half to recharge the tanks.....

Jason
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Old 10-02-2014, 04:29 PM   #4
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The only other on board users that I'm aware of is the suspension and front air tap. Those should only register on the top gage (sys 2). As the air suspension is"active", it could be possible on a bumpy road our in high wind, constant adjustments would be recognized through the gauge and dryer purge.

Remember, more air is pumped going down the road due to faster pump RPM. Not sure in my mind yet how that makes a difference here, though. Unless you had a fault unloader valve.

Perhaps others who work on these systems for a living could provide you better guidance.
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Old 10-02-2014, 05:49 PM   #5
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The top gauge is the one that always goes down while traveling. The bottom gauge rarely moves unless hard in the brakes but the top one will go down then back up when the compressor comes on. It may be the roads I assume. Noticed it more while I was traveling through DC and the roads were pretty harsh! Thanks for the info though!

Jason
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Old 10-03-2014, 10:17 AM   #6
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With the parking brake released, apply the brake and have someone listen for an air leak. You may have a bad brake chamber.

You may also need to have the air drier purge valve kit replaced. A leaking purge valve will allow air to leak out and cause the drier to keep purging.
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Old 10-03-2014, 11:48 AM   #7
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If I stop the coach and sit still the gauge never moves. It only goes down while driving. I can run the coach at idle with the brake set or not set and gauge remains full and not air discharge noise. Once I am driving down the road and coach is moving around is when I notice the air filling up every minute and a half. I have checked the lines and everything else and here no leaks. I guess my real question is, when driving down the road how often does your tanks fill back up? Or does no one really pay attention. I never noticed it until I was driving with the window open and heard it ever few minutes and wasn't sure if that is normal....

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Old 10-03-2014, 09:35 PM   #8
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The compressor should not cut in if the pressure is between 100 and 130 lbs. Once.the pressure drops below 100 the compressor will cut in and bring the system back up to high pressure cutoff at 130 lbs. When this happens you should hear air vent
.... just like on a city bus

All air brake systems are the sames although the absolute pressure will vary.
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Old 10-03-2014, 09:46 PM   #9
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If it only does it while moving and you have air ride suspension. It could be from the bags dumping and refilling as you hit bumps and dips in the road. This will use air and cause the compressor to kick in. When sitting still there is no dumping and refilling.
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Old 10-03-2014, 10:25 PM   #10
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Quote:
Originally Posted by JTN8 View Post
If I stop the coach and sit still the gauge never moves. It only goes down while driving. I can run the coach at idle with the brake set or not set and gauge remains full and not air discharge noise. Once I am driving down the road and coach is moving around is when I notice the air filling up every minute and a half. I have checked the lines and everything else and here no leaks. I guess my real question is, when driving down the road how often does your tanks fill back up? Or does no one really pay attention. I never noticed it until I was driving with the window open and heard it ever few minutes and wasn't sure if that is normal....

Jason


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2011 cadillac SRX
Don't have drawing of the compressor but one thing seems common. That is way too much cycling/leaking between no speed and operating speed. Wondering if problem is with compressor at full speed and leaking like a sieve, could shaft seals or internal valves be leaking badly with compressor at speed. Only common denominator that jumps out.
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