Problem with Air System

[dale farley]

Let me say up front, that I don't think there is a button I can push or something that simple to solve this problem. I've noticed that several times when I park the coach and level it, the right side drops down after a short while. The air pressure stays about 110-120 on the dash gauges for a couple days before they drop significantly.

It was really cold for Florida last night; went down to freezing about 10 p.m. and got to about 18 by early morning. When I went to move the bus at 12:30 today, I started it and let it fast idle for about 10 minutes. The temperature at that time was about 36.

The "Low Level" light went off as it should, and the air gauges were normal. I started down the road and noticed the right side of the bus was not running level. Pulled into a parking lot, shut off the bus, started the bus again, put the air control to the "Drive" position and waited for it to stabilize. It never did. I manually lowered the left side of the bus and tried to raise the right side, but it moved only a fraction of an inch. The best I could get was the right side off the ground about 8" while the left side was 12.5-13". Unfortunately, I don't know of a good place locally to check this out for me.

Is there a switch or valve that may be causing this?

Is that a chance I can get to it to replace it?

Is it more likely that I have an air bag leaking? Would my dash gauges still be reading 110-120 after several hours if I had a bag that was leaking?

If I have a sticking valve, could the cold weather make it worse?

Can I get Jon to bring his pit to Florida to help me trouble shoot and repair this?

I wish there was something goofy I was doing that might compare to the heater problem I really didn't have. I have an idea that this problem may have been manifesting itself in other ways, because the people I bought the coach from told me that they always lowered the bags all the way every time they parked. Of course, when you do this, you don't notice that the right side looses air. But this is the first time it has failed to go to the "Drive" position while running.

[Jon Wehrenberg]

Dale, There is no silver bullet when it comes to the ride height and leveling system.

Your description of outside conditions had bells going off in my head and I am sure others will chime in on this. Cold temperatures make your problems with the leveling system show up. Eventually you have the problem under all temperature conditions, but when it is cold you see it first.

The lack of response when you put it in the "road" position suggests something you should check. Make sure your coach air system is not filled with water, or at least there is not water in any of the valves. Open a drain valve on each tank. You should see a little water in the tank ahead of the dryer, but virtually no water on any of the others. You may have had a leveling valve (one of the Norgrens) freeze due to trapped moisture or water.

Lacking the opportunity to check other stuff that is my first guess.

If this condition persists when temperatures are above freezing, it could still be moisture, and your valves could be filled with water.

But if that is not the case, and I hope it is not, listen for leaks. Air up the bus, and shut the coach down, leave the key on and push the buttons to manually raise the side that won't come up. Step outside and listen for leaks.

If it will not come up, but you cannot hear any leaks the number of different things it could be range from a bad ride height valve (located in front of the drive axle fender liner), to a bad solenoid valve that is not switching the Norgrens to the closed position so the ride height valve can function, to a bad Norgren valve.

Once the moisture problem or leaks are ruled out then it is a question of methodically trouble shooting the system, starting with the solenoid valve pack on the rear wall of the steering compartment to the ride height valve to the Norgrens.

I do not envy you. Can you get a fellow POG member to help you poke around with this?

[Joe Cannarozzi]

There are ride height valves in a compartment in the area in front of the drives. If you get on the ground and look up in front of the drives you can see it. It has an arm attatched to it and that arm is hooked to threaded rod that comes down and is attatched to a piece of 1inch angle iron comming from the frame. The 2 lock nuts that attatch the threaded rod at a hole drilled in that piece of angle iron you can loosen, this is your adjustment for the height of that corner. lenghten it the bus gets higher, shorten it itll go down.

Remove the "adjustment rod' completly from the bracket and manually test that valve by moving the arm all the way up. That should make the bus go up. There is a slight delay built in so give it a few seconds. If this does nothing check the line that is suppling air by loosening that fitting and listening to hear if air pressure is evident.

If no air evident going in thats the problem, If you do have air in, the valve is bad. If I were to guess I would think the ride height valve is bad, its a little less that 200bucks, and not too hard to repair.

When you shut the bus off there is a solonoid that seals or isolates the air bag from the rest of the bus. If a bag were possibly leaking slowly that is why the guages stay up and that corner goes down while parked, however, because of the fact that it wont come up while motoring tells me its not a leaking bag because a leak that large would be very easy to hear.

Mango might have this procedure on his blog.

[dale farley]

I was going to try to eliminate the water in the system, but so far, I have not found the tanks. My maintenance manual shows one "Accessory Air Tank" located at the front left corner of the coach, but this doesn't sound like what Jon was talking about. I tried to see under the bus but was afraid to get under there too far since it might come down on me. I did notice that as soon as I shut off the bus, the right rear bag started going down. Unfortunately, there is no other POG member in this area that I am aware of.

[dalej]

Dale, it sounds like your in some cold weather right now, so it won't do much good to check for water in the tanks untill all thaws. If temps get in the 40s you can check. If it got down in the 20s the lines will freeze if there was water sitting in the sagging part of the lines. You will know when it thaws, the bus will air up again.

There are two tanks above the drive axles and one above the steer axle. Again it won't help cause the frozen part will be a line, keeping air from passing.

[Joe Cannarozzi]

If its leaking down that fast you should be able to hear air escaping. That very well could also be an air bag or line to it if its going down that fast.

There are 2 more tanks at the drive axle on the frame rails. If you feal mechanicly inclined- raise the rear all the way up and block out the frame on both sides, prefferably a couple of 20Ton jacks or some OAK, crawl in there and drain. Jon has pics. up on the correct procedure and locations.


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558

We replaced our drains with these enabling us to drain tanks easily and often.

We will also be going through the panhandle inbetween Christmas and New Year and Ide be more than happy to help you with whatever I can.

We usually fuel at the Flying-J, Midway, I think its exit 192, but we can also come down through Dolthon, Al. on 231 that puts us on I-10 at the 100mm or so.
Let us know we would love to meet you.

[Joe Cannarozzi]

Dale,
Did you ever happen to notice how often the air compressor starts and the air dryer "SNEEZES" while your driving?

Do the air pressure guages stay up while driving or are they constantly going up and down inbetween100 and 120?

[Jon Wehrenberg]

I think Roadrunner's problems are related to a leak. He and I passed a couple of emails and he mentioned he could see the right side going down, so from that it sounds like he can get it pumped up, but the leak is so bad it goes down right away.

As Joe says, he should hear that. Unless he has a safe way to raise it and block it up I am concerned about trying to get under it to get closer to the source.

Roger had a leak in one of his front air bags, but could not find it until he got under it and soaped it from the center of the bus between the wheels. But with Roadrunner's fast leak down, he is probably going to hear it, if not with his ears alone, but with a stethoscope aimed in the general area.

The problem is the leak can be a valve, and air bag, or less likely a fitting.

That does not suggest he does not check his system for water. On my 40 foot I had two tanks in the rear over the axles, one in the front over the axle, and one inside the steer compartment.

[MangoMike]

Whoa!

What happened to all the replies since Jon's this morning?

MM

[dalej]

I think the server is getting switch, I have posted two times and nothing showing up. Maybe I have been tagged!;)

[dalej]

I also ask if anyone was bidding on the 01 Prevost on Ebay and nothing...As Jerry says..."whats up with that"

[Joe Cannarozzi]

Any members who own a coach and have not either put a new style spin on cartrage on the air dryer, or, on the older style removed it for a rebuilt replacement, on 2 year intervals, are making a mistake.
The folks with the new busses have all kinds of phnewmatic devices to destroy, dont take that chance. All these things are just full of little plastic and rubber pieces very prone to breaking or distorting from frozen moisture.. Everyone seems to understand the importance of getting the water out of the plumming system. The air system is no different for all the same reasons and MORE.
Ours was 179$ rebuilt/exchange and a rebuild kit is 79$. Any honest shop should charge mabye 2 hours labor, pretty cheep insurance and piece of mind if you ask me.
In the colder climates when your forced to shut down due to air related problems, due to cold, you at that point also loose the advantage of those warmer opporating temps. and the problems snowball from there.
Our 86 is alot less complicated in this area and still we replaced, due to water damage: 2 ride height valves, parking brake valve[the button], both auto hight valves in the seats, a wiper motor, the belt tension shut-off, a belt tension cylinder, a warning sender/valve, and the air dryer. I still get an "oily mist' out of the bleeders and I have been draining our tanks at almost EVERY time we stop, and then some. Once you allow water, and oil too with a old compressor, into the system it is very hard to get it out. They have air brake antifreeze, that is alcahol based but I dont think it would be wise to use it, you will smell fumes venting from the exhaust port of any air accessory each time you use it.

I know I have already posted the same suggestion elsware but I think its worth repeating.

[MangoMike]

Joe,

Good post and advice. Where do you get the lanyard pulls for the drains?

Dale,

You would look good in that '01 XLII my guess at 250k it's a pretty damn good deal, especially w/ the car. I think the mirrors are blue to hide the corrosion on the Crapco Mirrors that plague us all.

MM

[dale farley]

Joe,

I had problems getting into the forum last night, so I haven't responded to anything. I really haven't noticed how often the dryer sneezes when traveling. As far as I know, the air pressure stays between 100-120 most all the time when running. Several times when I have turned off the coach, the air gages have stayed at about 110-120 for a couple days without a significant loss.

You mentioned coming by during the holidays. I am probably a little farther out of the way than you were thinking. I am on Hwy 29 that connects Pensacola to I65 in Alabama. Hwy 29 is exit 10 off I10, and I am 13 miles North of Interstate 10.

I am going to try to get under the bus and drain the tanks then see if I can actually spot the leak in the rear. If I remove the tag axle will I be able to get under far enough to see the tanks?

[MangoMike]

Dale,

When you get ready to get under the bus you need a couple of these. Air powered 20ton bottle jacks.

http://www.prevoman.com/Pages/Cool%20Toos/jack.jpg

Fast Roger turned me on to them and they were just a little more than what I paid for manual ones from Craftsman.

More info here:

http://www.prevoman.com/Pages/Cool%20Toos/ToolsPg1.html

[garyde]

Hi Dale. My manual says to check and drain those tanks once a year during service. The front valve in the steering compartment should be drained 1st I believe to check for water. The other small valve in the back compartment @ last bay starboard, can be drained as well.
If you have not been following these threads regarding jacking your coach up, I would not get under it. Gary

[Joe Cannarozzi]

Ill deffinatly agree with Gary with crawling under.

Gary I think that once a year service your being shown is based on the premice that we opporate and maintain a properly functioning air dryer to allow this. Even with that said I would NEVER go a whole year without checking the air tanks, if for no other reason, its just too easy.

Does anyone know what Bendix suggests as a normal service interval for the new spin on cartridges for the newer driers? Ill venture a guess, annual under normal conditions and more frequently as needed?

Mango, you would probably benifit if you could find and ask a local carrier or trucker where they get parts like brake drums, shoes, and general truck parts supplier, filters, hoses, valves ect. Ill be happy to send you some of those drains if you cant find any locally or even if you dont want to search, let me know.

[Jon Wehrenberg]

Joe, The Bendix recommendations for air dryer service vary with the type vehicle. For motor coaches I think the interval is two years as you state.

This site is a great one for learning about our air systems. Every one should bookmark it. You can navigate it forward and backward.

http://bendix.com/bendix/troubleshooting/index.do

[JIM CHALOUPKA]

Just wondering do these busses use an air dryer with a desiccant that must be changed periodically or is it one based on the refrigeration principle?

[Jon Wehrenberg]

The air dryers are dessicant type.

[truk4u]

My post got lost this morning for Roadrunner, remember, the dash gauges are for brake only and do not indicate any aux air pressure. Your air bag air is coming from the aux tank.

[Joe Cannarozzi]

The air bags are "service air".

We have 3: emergency air, service air and accessory air. The 2 guages, primary and secondary are in fact, emergency air and service air and the service air supplies brake application as well as suspension. When we park and "level' it might then be supplied by assessory air, Im not sure, but going down the road-service, or secondary I believe, is feeding the suspension. On ours the accessory air feeds wipers, seats, door lock, belt tensioners, leveling and waste dump. Emergency, or primary air is exclusivly for releasing the emergency brakes.

[truk4u]

Joe,
Unless they did something strange for your vintage, the suspension air is independent from the brake system. The brake systems has two tanks, a primary and a secondary and nothing else is supplied from those tanks except for brake application. Here is a quick flow chart:

Compressor - Dryer - Wet Tank - Primary Brake - Secondary Brake - Auxillary Tank

Wet Tank - This tank sometimes has a different name, but the purpose is to provide the source of air pressure for the governor/dryer. This tank is the one you can manually fill from the starboard side engine compartment air valve. This manual valve fills all tanks.

Primary Brake Tank - This tank pressure will be one of the needles on your dash or in some, a second gauge.

Secondary Brake Tank - This tank pressure will also be on the dash and is sort of the back up to the primary if it fails.

Auxillary Tank - This is the last tank in the chain and supplies air to the suspension, belt bellows, pocket doors, sliding step, generator bags, etc. You can fill this tank manually in the steering bay with the air valve. Mine has a pressure gauge and some of the lucky guys have a gauge on the dash for this tank.

Seated Prevosts with a Kneeling Feature, it lowers the front for easy entry for people like Harry and Lew, has it's own tank also.

Hope this helps......

[Joe Cannarozzi]

Tom , thank you for that post. We all continue to learn. Lets go further. Often times ours sits long enough so that ALL air is gone, suspension, everything. While airing up the 2 guages go up togeather until about 60 then the secondary hangs back and it seems to me will only continue on its way up coinsiding with the bus after it comes up to height?

Hopfully,common sence would tell you the brakes are seperate for safty sake. I was under the impression this was acheeved in a different fashion, air valves. We have a schmatic on the rear doors and Prevost colorcodes those systems nicley. Im gonna go see what else I can learn.

Sorry for that previous post if it was wrong.

[jello_jeep]

For what its worth, on mine I have a dash switch for the aux air compessor. There is also a small green pilot light that indicates when the aux air compressor is on.

If mine has been idle for awhile, if I push the switch in, the compressor will start and air up to its cut off point.

However, if the air leveling system is on, if it wants air for any reason, the aux compressor will come on no matter if the panel switch is on or not.

My aux compressor is not the micro type in the shoe box below the driver's window, mine is a larger unit mounted on top of my generator. From looking at the paperwork, it was an option to the original owner.

Not knowing any better, I had assumed that the suspension system drew air from the engine compressor system unless you were stopped. Glad I was reading all this!

[Joe Cannarozzi]

So both primary and secondary feed Yellow, redundently? Looked like the suspension was seperate from the accessories. Probably just in color but they both have the same source?
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The other diagram on the door was tag axle plumming, not complete.

[Joe Cannarozzi]

Warren,That aux. compressor that you are talking about is not required to keep the suspension up while motoring, but just to supply air to the accessories while parked.
Sorry for the confusion. Looks like I,m the guilty one.

[truk4u]

Joe,
Looks like we need to learn how to speak/read French:eek: I think your right, the source is the aux tank but the lines are different color coded. It's no wonder we drive ourselves nuts over leaks when you look at the schematics.:confused: I was just bragging a few days ago that mine was setting nice and level with no problems and whamo, this morning it's on it's freekin nose.:mad:

Warren - How about a pic and more information on that compressor, I want to add one to mine.

[Joe Cannarozzi]

Ours is a Dayton, oilless type. Very SLOW, WEAK.

Ive thought of uprgading too. Got plenty of room to play around with at that spot. Something like Dalej did.

[jello_jeep]

Sure Tom, be happy to. It will be the week of Christmas though, as the bus is in beautiful Lake Havasu City AZ. We are fixin to go down there that week so I will snap a pic for ya'll and dig up the informationi on the compressor.

[rfoster]

574Once upon a time (I searched for it in previous post, but did not find) there was a post by yours truly that I could not get my air bags to raise the coach from the shop air compressor. Not so, I was just too impatient and Yes you have to have the Key in the on position and the 4 buttons in the manual and up positions. It is amazing to see 48,000lbs being lifted by 115 lbs of air pressure. But I have always been amazed by a Prevost! My bus will leak all the aux air out in day or less due to leaks, I can plug in my shop air and continue to raise coach to the max height (without starting the engine) in a matter of a few minutes. This is a plus when inside closed quarters.

[Jon Wehrenberg]

Everybody needs to realize aux air discussions are converter specific and even further, may be production date specific.

My 87 Liberty could be leveled automatically or manually without the key being on. My 97 Liberty requires the key to be on.

Not all conversions have an automatic leveling feature and not all conversions have a converter installed aux air compressor.

For those relatively new to Prevost ownership, do not consider all comments about the aux air systems to be correct relative to your coach.

[dalej]

I think that's one of the beauties of the coach's aux. air to raise the coach without the Detroit. I look at it like our bus has air jacks. When in the bus barn I just don't like starting the engine. Even in RV parks I like using the aux. air to raise the bus to ride height, so I don't have to have a big diesel running when parked next to someone.

[truk4u]

Glad you worked it out Dodger, that's exactly what I do. Here was my pic from that post you couldn't find...

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