Is this an aux air problem?

[Devin W]

Posted up an intro in the noob area and here is the first of many questions that I'll be posting.

We just got back from our first trip which went well aside from the fact that we couldn't flush our microphor toilet unless the engine was running.

I'm under the impression that this would be an aux air problem based on the fact that my door air lock, the sliding stairwell floor, the dump valve and the toilet would not work unless the engine was running. I had several leaks on what I assume be the two primary air systems when I had the engine serviced a couple weeks ago because the suspension would leak down within an hour and I couldn't do any technical maneuvering that required tapping the brakes alot without the brake system losing pressure. Those have been corrected and the system 1 & 2 air gauges on the dash can be showing between 100 and 120 psi, but none of those other air operated amenities would function until I started the engine.

I have turned on the aux compressor, but it just seems to run non-stop (never reaching a shut-off point) and it seems that it actually causes the main air systems to leak down when I have it running.

I'm sure there is some important info that I'm leaving out, but I'm not sure where to start even if the consensus is that this is an aux air problem. I know where the aux compressor is and what I believe to be the regulators (located under the drivers seat near the steering), but how do these air systems interface with one another and those air operated accessories. I don't see any gauges or way to determine what limits the run time / pressure on the aux compressor (it started running non-stop after our trip home from purchasing the coach, but didn't cycle like that during our inspection and test use).

OK -- bring it on!

[garyde]

Hi Devin. It sounds like you have a leak. The list of things it operates; Isri Drivers seat, floor slide, pocket doors, toilet, bed lift, generator air bags, Fan belt, & possibly train horn. This is seperate from the other air systems. Some owners have put a guage on the regulator to verify the system is holding air.
On my coach it also inflates the slide seals.

[Jon Wehrenberg]

Devin, welcome to the asylum. We are here to answer your questions, and occasionally the answers we give will be correct.

You may not have realized it, but you have a leak. (Just kidding, you apparently know you have a leak.)

Ignore the toilet for a moment because that does not appear to be the problem. It sounds like the leak is so large I suspect you should be able to hear it. Just to be certain your bus is roadworthy, and the leak is in the aux system do a DOT brake check. Turn the engine off. You should be able to engage your service brakes, and except for the small pressure used for the brake application, the two air systems should not drop. If that checks OK, chock the wheels and relase the emergency brake. Again you should see a small pressure drop and then the gauges should show no further loss of pressure. Everybody should be doing this brake check prior to any travel. The final check is to fan the service brakes, and at some lower pressure, 60 or 70 pounds you should hear the audible alarm and the warning light should come on. At 40 to 50 pounds the emergency brake knob should pop back up.

Now we return to the main problem, assuming the brake system checks OK.

Bring up the air pressure by running the bus and as soon as it is at max pressure, turn off the engine and listen. With a leak so big the aux compressor will not keep up you should hear the leak. If you cannot hear the leak your job just got much harder, but there will be no shortcut. The leak must be found.

Just for your own information, I believe your bus has a suspension system that requires you to maintain aux air pressure of at least 35 PSI at all times or the valves back above and between the tag and drive axles will dump air from the rear air bags.

There are so many potential points for leaks nobody here can point you at any specific likely starting point. Once you can pinpoint the leak area, even if you cannot see it, let us know. We can probably help with fuirther info.

[dreamchasers]

Devin,

Welcome to POG!

I can relate to air leaks, especially when I noticed the leaks after I purchased my coach. I have a 1995 Country Coach, built on a 1994 chassis. So our chassis configuration are close.

First, the two gauges that you see on the dash are air pressure for your braking system, primary and secondary. The primary is for the rear brakes and the secondary for the front. A special "shuttle cock" valve will protect each side from a failure from the other. Additionally, the air system is designed such that if you have a leak in either, all air will service these systems.

You mentioned that your suspension leaks down within an hour. Well, on you vintage coach, same as mine, the rear tag axle will release (the air bags that hold the tag axle weight) if you aux air pressure drops to the 60 - 70 pound region. This is because our vintage requires air pressure on the Norgren air valve logic to hold the tag axle in the down position. This logic was changed in the ~1995 chassis. This item can be very confusing.

If the leak you describe in your suspension means something other than the tag axle release, then you have a leak in other areas. It is important to remember, that with the key turned off, all air is blocked to the wheel air bags, except for the tag axle as mentioned above. So with the coach air system pressured, then the key off, the coach should maintain that position.

If you are losing air pressure in one of your braking systems, the results should be, the tag will release and coach will settle down in the rear.

The suspension is dynamic and required a considerable amount of time and effort figure out. Trying to troubleshoot suspension leaks in an email is difficult to impossible.

When I first bought my coach, the Prevost air system confused me to a point that I developed a dynamic software driven presentation of how it works.

http://forum.prevostownersgroup.com/...ht=sevierville

You can experience leaks in the air system by exposing the coach to low temperatures and higher elevations. For example, my coach developed a leak when I visited Leadville this year, but will sit for days with no pressure lose while here in Texas. The temperature differences will shrink the metal/rubber components with the temperature differences.


Within the POG membership, their are members that have much experience with the Prevost air system and can offer you more help.

I will send you a private message with my contact information.

Good Luck!

Hector

[Jon Wehrenberg]

Hector is being too modest. Nobody knows the suspension system as well as he does.

I do want to make one thing clear. The leakdown of the suspension system is not the problem, but is a symptom of the problem. When the aux air drops, it in turn causes the suspension to exhaust air as Hector has described.

If you cannot hear the leak here is a tip that may help isolate it.

Your Liberty has a manifold in the lower steer compartment. All of the house systems are supplied aux air from that manifold which may have as many as 6 air lines coming from it. I would suggest you disconnect and plug the air supply to the mainfold to see if the bus holds aux pressure. (you can check pressure with a tire gauge at the valve located on the rear bulkhead of that compartment.

If the aux air holds the leak is in the house side and by removing and plugging the mainfold at each air line you will find which circuit is the leak.

If the aux air pressure drops with the aux air to the manifold plugged, focus on the bus. That could be the door air lock, the belt tensioners, leaks at the solenoids that control the suspension, etc.

My guess is like the rest of us, unless and until you chase them down you probably have numerous small leaks that have occurred over time and were neglected.

[ajducote]

Devin,

Welcome to POG.

If the AUX air leak is large, using a helper, try putting a high volume shop air to the valve in the steer compartment and walk around the coach and listen for the leak. That is how I found a large leak on my tag axle lift chamber. Try to have as little background noise as possible and you should be able to find the general area of the leak.
Good luck

[truk4u]

Devin,

Your aux compressor is behind the two cruiseairs in the front bumper compartment and can only be accessed under the bus by removing an access panel.

Look at my post and you should have an aux pressure gauge and quick disconnect in the steering bay for filling the aux tank. It's easier than running the engine.

http://forum.prevostownersgroup.com/...=aux+air+gauge

Also, if you have a leak that bad, then your engine compressor is running almost continuously while driving and you would hear the air dryer popping off everyone few minutes or worse.

If you need help, feel free to call me at 770-634-7530 since we have the same year bus.

[ajhaig]

Whatever you do... Do NOT crawl under the bus!

[BrianE]

Devin, Welcome to POG. I noticed that both Tom Truk and Hector (Dreamchasers) posted their phone numbers. Both of them, Jon and various other Poggers are VERY knowledgeable.

AJ advised not getting under the bus. If you have mechanical skills and want to fully understand your bus systems you will eventually need to go under. The bus MUST be jacked AND properly supported so that you are absolutely not depending on the air suspension system to keep it elevated. Details of where and how to support the bus are best explained via direct contact with someone who is very familiar with the process. PLEASE avail yourself to the offer of help.

If you have no intention of accomplishing your own maintenance be sure and visit a Prevost maintenance facility and request that a senior mechanic brief you on the under the bus components while it is on the lift. Hand him a flashlight and take notes. Understanding how things work is the best way assist them in trouble shooting future problems and to help you avoid unnecessary repair bills.

The under the bus components are almost identical to those of a modern semi truck. Once safely accessed they are fairly straight forward and can be worked on with some guidance from Prevost maintenance manuals, telephone assistance from Prevost Field Service Representatives, and advice from the membership.

Additionally, be sure to use the Search feature of the forum and click on the bus logo at the top of the forum page and check out the Articles and Information Sharing sections of this site. Many of your questions will have been discussed and answered before.

Good luck, the adventure begins.

[Jon Wehrenberg]

Andre,

I don't want ot hijack Devin's thread, but how did you detect air from the tag axle lifting chamber? Did you suspect it and then lift the tag. It is my belief the tag lift chambers never see air unless the tag lift is engaged.

Just curious.