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! :D

[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/showthread.php?t=2116&highlight=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/showthread.php?t=3914&highlight=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.

[ajducote]

Jon,

I could not build air pressure when the tag was lifted. Any time the tag was up, the aux air compressor would not quit running. So I put shop air on the valve in the front compartment and walked around until I heard air. Sprayed soapy water and the tax axle lift chamber made big bubbles. See this link for the cause.
http://forum.prevostownersgroup.com/showthread.php?t=4094

[Jon Wehrenberg]

That answers the question. I couldn't figure how you would know the diaphragm was leaking unless you were trying to lift the tag.

[garyde]

I remember Tom had air leaking when we had is Coach up on the lift in Oklahoma. Was that a tag leak ?

[truk4u]

Gary,

The leak quit while on the lift and I haven't been able to duplicate it. I have since raised the tag and monitored the aux pressure gauge and no leak down.
It's still a mystery!

[Jon Wehrenberg]

I don't know if others have had this issue, but on occasion the pressure relief valve on the engine driven compressor will leak. It seems to occur only when I bring my bus air pressure up via shop air instead of running the engine.

It makes a sound audible to my ears alone, but will stop after a while. None of my air systems (aux or the two braking systems) appear affected.

From trying to chase the source of that leak I know it sounded like it was coming from the radiator side of the engine, and it was only through the use of the stethoscope was I able to pin point it because apparently the sound echoes throughout the engine area.

[treedoc]

Just courious Jon why do you bring up the air in your coach with shop air? Also would your pressure releif valve leak due to too much air form your shop compressor? Rick

[Devin W]

Thanks everyone for the great info and responses. I have noticed that I can hear what sounds like air leaking/seeping from somewhere in the steer bay, although it seems like it is coming more from the curbside under the stairs. Maybe the fitting for the floor slide needs to be tightened. I didn't have time today to play with it, but if the sun comes out tomorrow then I may brave the cold long enough to drop the front bumper down so I can see if I can access the leak.

I sprayed all of the other fittings, couplings, etc. near the steer bay door and all seemed to be "air-tight".

Tom, I don't have an analog gauge like you do in that compartment, but I particularly like the digital gauge that you installed on the dash to monitor the aux pressure. I may do something like that. It could be a good project for when I'm in Houston over X-mas where it will be a bit warmer!

How does the compressor know what pressure to maintain in the aux system? I didn't see any way to set a pressure or where there may be a sensor on the aux air fitting that monitors that. On the sys 1 and 2 fittings, it's pretty evident where the sensors are for the gauges.

[Jon Wehrenberg]

Just courious Jon why do you bring up the air in your coach with shop air? Also would your pressure releif valve leak due to too much air form your shop compressor? Rick

Rick, If I am working in my garage, rather than run the engine just long enough to build pressure I just air it up from the compressor. I have a big one and it is always up to pressure so it is fast and easy. No I do not over pressurize it. I usually air it up so I can chase a leak or raise or lower it depending on if I am going to work on it from the pit, or if I want to drop it down to clean it. (You need aux air to work the Norgren valves to make the bus go up or down)

Short time running of the engine is not the best thing you can do for your coach. If you are going to run it, it is always best to run it long enough for the engine to come up to temperature and to get hot enough to evaporate any condensation that may collect.

[Jon Wehrenberg]

Thanks everyone for the great info and responses. I have noticed that I can hear what sounds like air leaking/seeping from somewhere in the steer bay, although it seems like it is coming more from the curbside under the stairs. Maybe the fitting for the floor slide needs to be tightened. I didn't have time today to play with it, but if the sun comes out tomorrow then I may brave the cold long enough to drop the front bumper down so I can see if I can access the leak.

I sprayed all of the other fittings, couplings, etc. near the steer bay door and all seemed to be "air-tight".

Tom, I don't have an analog gauge like you do in that compartment, but I particularly like the digital gauge that you installed on the dash to monitor the aux pressure. I may do something like that. It could be a good project for when I'm in Houston over X-mas where it will be a bit warmer!

How does the compressor know what pressure to maintain in the aux system? I didn't see any way to set a pressure or where there may be a sensor on the aux air fitting that monitors that. On the sys 1 and 2 fittings, it's pretty evident where the sensors are for the gauges.

Devin,

The topic of air leaks, how to find them, where they might be, the aux compressor, how pressures are regulated, etc. is difficult even if all of us have the same conversion. The complexity of the issue goes up exponentially as we are faced with upgrades made by the converter (your Liberty and mine may not have the same compressor for example), changes made by owners over the years and differences between other conversions and ours.

But we might be able to generalize. Often our aux air compressors on Liberty coaches use what looks like a well pump switch, mounted on the rear wall of the steer compartment bulkhead. It is adjustable and the range may be anywhere from 40 on to 80 off to 80 on to 100 off. Most I have heard of use the 100 PSI upper limit.

Finding air leaks is more art than science. Amongst this group we use our ears, soapy water, stethoscopes and ultrasonic leak detectors. None of the previous work for all leaks, and each method has its strengths and weaknesses. If you turn your coach over to someone and ask them to make your aux system leak free for example, it is likely you have just paid for someone's kid's college education. I'm only half kidding.

If you can hear the leak, you will recognize it is hard to pin point its location because of the ability for a leak over here to sound like it is coming from over there. The next step is to spend $5.00 at Sears on a stethoscope which when pointed at the leak amplifies its sound making it easier to locate.

There is not enough space or time to provide much more on this but as you play around chasing leaks post your findings and the inmates of this asylum we call POG can offer advice and tips.

BTW, If you think the floor slide is a culprit locate the air line feeding the solenoid valves that operate the slide and cap the air supply to them. The air leak should go away. The cylinder is serviceable, but before fretting over that the best bet is to prove that is the problem, or at least one of the problems.

[truk4u]

Devin,

Jon already mentioned the aux pressure and it being adjustable. If you think the leak is the floor slide, just put it in the out position and with the door open, you can get to the air cylinder and squirt it with some soapy water. It sounds to me like you have more going on than the floor slide or else your aux compressor has a serious leak. Keep looking, you will narrow down the leaks, but you'll never be leak free!:(

Here's a few general places to look for aux leaks with your vintage:

Steering bay
Floor slide
Generator bellows & regulator
Grey water by-pass cylinder
Waste tank dump cylinder
Air horns
Toilet - if it's air like mine
Aux compressor & fittings

[Danss]

I have had two air tanks fail with pinholes. Check it. Dan

[treedoc]

Tom If a coach is leak free from the factory ( I presume ) than why can't it be leak free now? Jon I find it rather odd that the relief valve will leak one way but not the other! Air is air. It would be interesting to know the answer to that puzzle. Rick

[treedoc]

Tom If a coach is leak free from the factory ( I presume ) than why can't it be leak free now? Jon I find it rather odd that the relief valve will leak one way but not the other! Air is air. It would be interesting to know the answer to that puzzle. Rick

[truk4u]

Rick,

I suppose if someone wanted to replace or rebuild every fitting, norgren valve, air cylinder, air line, air tank, "O" ring, etc., you might get it tight, but by then I'll be too old to drive and the guy doing the work can retire!;)

[tdelorme]

Devin, look in the steer bay and see if there is a shut off valve for the step slide. My 91 Liberty had several needle valves in the steer bay for the step slide, pocket door, sewer dump, ect. My 2000 Liberty does not have the needle valves so your 94 may not either. Anyway, if you do have a valve for the step slide air supply, see if the leak goes away when you shut the valve. If it does, I'm gonna bet that the step slide cylinder is going to need replacing or rebuilt. On the 91 Liberty, it was a huge job replacing the cylinder because Liberty attached the cylinder to the back edge of the step slide. At some point, they started attaching the cylinder to the front edge of the slide, so like Tom says it can be accessed from underneath when the slide is out. If the cylinder is attached at the rear of the step slide and needs to be replaced, send me a PM and I'll go into detail on the fix.

[Jon Wehrenberg]

Tom If a coach is leak free from the factory ( I presume ) than why can't it be leak free now? Jon I find it rather odd that the relief valve will leak one way but not the other! Air is air. It would be interesting to know the answer to that puzzle. Rick

I didn't say it wouldn't leak if I pressurized the system using the engine driven compressor.

When I start the engine I am usually going to drive away and with the engine running there is not way to hear a leak. However if I shut down for lunch at a rest stop, I don't notice it, but then again is is noisier at a rest stop than it is in my garage. I think exercising things makes them work better so that might be why it is not noticed when the engine is compressing the air.

[MusicianTrader]

This was an amazing read for me. Answered all my questions and solved some riddles for me.
thank you very much

[Ck2hans]

Took me about 1 year of part time playing around with all the air system to fix most of my leaks. To date I have replaced all air bags and changed fittings to compression from push in, changed all brake chambers, Camper Joe changed all Norgren's and again changed all push in fittings to compression's, replaced valve on horn, replaced PSI regulators on generator air bags, replaced belt air bags on engine, replaced brake relay valve's, replaced directional valve for air sliding door to bedroom, changed all push in fittings on front bulkhead to compression.

In the process of trouble shooting, I installed ball valves to turn off the driver's air seat, air horns, sliding floor at entry, sliding door to bedroom, air bags for generator, and aux air supply.

End result was/is brake system will hold air in storage for a month and a half. Aux air WAS holding air up to 18-20 hours. The aux air is back to leaking down in a 4-6 hour time frame, even with all the various aux air feeds turned off with the ball valves I installed.

I have kind of excepted there will be leak downs in the aux system. Maybe someday when I get bored I will go back at it and try to find the remaining aux leaks

Chuck

[Joe Camper]

Ya know Chuck sitting static with the emergency brake applied to have the brake tanks stay up for a month is very very good.

However the real test would be wheel chocks in place emergency brake released and a weighted object on the brake pedal. I think if u did this u should see the same results or something is leaking. In this configuration u r supplying air to the emergency diaphragms and the service diaphrams both.

This is a test everyone should do at the end of every day.

[MusicianTrader]

as soon as i am able too I shall start with fittings as well. Seems like alot of work you did for it to eventually leak again....so i will not go all in like that. If i can get aux air to come on every 4 hours that would be a huge win for me!. my current aux air is a shytty 12v that is shot...only puts out 10psi. I currently have my Kobalt compresser in engine bay connected to 110. i flip the switch in bus when i need air for my toilet and tank gate valves. im gone for work 12 hours so we are talking min use. My bags hold air...they are brand new with all the valves (prevost hou)

[Ck2hans]

The just I get from this form and others is; If you ever do get all your air leaks stop, don’t plan on it lasting…
Chuck

[Joe Camper]

Chuck Pat if he, you, just gets a tag axle logic instalation that combined with the void of any essential aux air accessories on the house side on your conversion even if u can't keep aux air up it won't matter. Only run the aux air compressor just before start up for the belts.

And Pat full timing like u do makes it even harder to get more airtight. A nice quiet garage makes a way better environment for this task. U will need dead calm out in the country or the ultrasonic pick up wind and wind also blows away bubbles and champagne bubbles r not allowed to icubate and expose the very small leaks.

Let's say u r going down on 1 corner an 1/8 to 1/4 in over 24 hr. In a week that's a observable lean but a tiny leak. That's a very small leak that only if soaped up good and directly over hrs of time will develop very small mound of tiny bubbles " the champagne leaks" . u would be lucky to find that with a breeze blowing away and drying out the dousing and then other normally occuring sounds.

Get the 3 corners of the suspension air tight and install tag axle logic then just do the best u can with aux air leaks.

[Joe Camper]

Chuck u do a great job with yours. When u r fueling ask around, ask driver's how much air their rigs hold and for how long. It will make u proud. Very very very few r buttoned up tight all around. This crowd goes way beyond the average companies and operators with safety and preventive maintenance with way more complicated rigs, in my opinion.

My Pete is far from perfect. I drop 1.5 lb per hr . if I shut down at 125psi when I wake I'm still north of 100 and I think that's pretty good. And it is good. I constantly sweep it and get nothing. But I keep doing it. That's the way it is. They don't need to be perfect just close is fine.

If this same loss was under the scrutiny of the dot. They would conuct a 10 min test. Well in only 10 min it's barely going to move the needles at the current rate of loss they will conclude it's almost perfect in A+ territory and on the other hand if leaking way worse I would be legally allowed to loose up to but not to exceed 1 lb PER MINUTE and pass the test be allowed to continue on.

They would require u release the emergency brakes and depress the brake pedal with your foot and hold it during those 10 min.

Every one of u should be doing this same thing at the close of every day traveled. Not 10 minutes but shut down put wheel chocks release the parking brake bus off and walk around back. Emergency air leaks start slow and small u will never here it driver's seat bus running but the first day a slight leak begins u will catch it with this habbit. Then if quiet go step on the brake pedal and hold it and listen. Bam emergency air test followed by service air test. U would never go down the road with a brake system air leak without spotting it very very early on when it still can be conveniently managed and repaired safely if u do this.

And quit loosen sleep when they r damn good like most of u guys r.

[PrevostNewbie]

Chuck, what does that mean someday when i get bored? I think you mean when you get to that item on your list?

[Ck2hans]

You make a good point Mike :o
Chuck

[MusicianTrader]

Very good point Mr Joe. Time escapes me too, was just notified yesterday we are moving to the dreaded 7day/12 hour schedule starting today.
Have a great day everyone