[Jerry]

John, this is speculation, but it is based on a similar problem I dealt with several years ago on a coach.

It sounds like you have verified the rotary switch and the rocker switch are getting power and that power is getting to the solenoid manifold stack. It also sounds like you have or can easily verify when those solenoids get the electrical signal they are opening and sending air pressure to the various Norgren 3 and 5 port valves that control the level low functions.

The next step is to verify the air pressure from the manifold is reaching the appropriate Norgren valve. The service manual and pneumatic diagram accessible from the Prevost Car site will help you identify which valve should be getting control air pressure, and where the valve is located.

If you have required pressure to the valve plunger or actuator port the spool inside the Norgren valve should shift and open or close air flow as required.

Your problem in my opinion relates to the air supply Norgren and it is possible your pneumatic system has or has had a moisture or water problem and the Norgren that is causing the problem may be hydraulically locked or may have built up corrosion (like a paste) preventing the valve from shifting.

There may be another cause, but if you start at the switches, verify the solenoid manifold operation is correct, and that air is getting to the associated Norgren valves you will have along the way identified the problem.

[Archived]

On another Prevost forum I wrote a long narrative of my adventures getting my 97 to behave as I thought it should. Similar issues to what you describe – would go down but not up. Turns out mine simply takes a long time to pass enough aiair to raise the bus. so, here goes a short version.

each converter does different things to/with the Prevost level low system. Mine, CC, adds an auto level that simply sends electronic signals to the level low solenoids mimicking what the rotary dial and rocker switch does. But it only works with th key off.

the surprise element for me was how long it takes to pass enough air to raise the front as both bags have to fill at the same time. The Prevost air max regulator (the sneeze valve you hear) shuts off the compressor at near 120. To raise the front can take 100 to 110 for around two minutes. If you have the high idle on the air pressure build to the point the compressor turns off can happen before the bags get enough air to raise the bus past ride height.

Try low idle instead. Air fills the brake tanks first and only then will spill over to supply air to the bags and the aux air system (somewhere around 80 psi). With the rotary switch set to front and rocker switch set to raise wait for air pressure to build to around 110 on low idle. Then keeping everything the same press the brake a couple of times to drop air pressure to around 90. That will turn on the compressor again. Repeat if necessary and see if your bus eventually raises in front. You just have to be in that 100 to 110 pressure zone long enough to supply enough air for the bus to raise.

it may be there is nothing wrong with your bus at all. If there is a problem with the five valve manifold, my suggestion is replace them and the solenoids all as a set (around $500 when I did it) rather than trying to ID which one to change (around $200 each). Once the new manifold and solenoids are installed take the old ones apart, clean them, test each solenoid and save them as spares

Jerry

[Jon]

The pressure protection valve will assure brake tanks are filled first before auxiliary, but high idle is a quicker method as the compressor builds air quicker.

[Towson]

Thanks guys. All makes sense. Jerry I am gonna do just what you say later today to see if the pressure range may be at least part of my issue as well.

[DON]

While some coaches are slow to rise it has to be understood Norgren valves that have been impacted by moisture in the pneumatic system can be partially opening resulting in slow operation. It also needs to be understood if the coach axle weight is greater than the Prevost weight limit the coach will be slow to respond. Usually when the slow response is an issue it is in the front only because of excess weight.

If the coach comes to normal drive height relatively quickly it is bypassing the Norgren valves (to an extent) and the air is passing through the ride height valves.

Generally speaking converter supplied level low systems piggy back on the level low and only control the solenoid valves on the manifold that are also controlled via level low. Nothing past the solenoid valve manifold (except the Liberty added Norgren exhaust valves) are converter installed that I am aware of.

[Jerry]

Mae west vs double flare airbags, REMEMBER? I’m surprised to be the first one here to mention this: for yrs Prevost Parts was selling the wrong replacement front airbags. The wrong front airbags will NOT raise the bus above normal travel height. Here is a PC thread link about it: Link

[Jim/Chris]

I found no moisture damage in any of the Norgren valves I took apart. My front measures well below the weight max on the fronts as well. I also found using high idle worked to more quickly reach 80 psi, but went from 80 to 120 too fast to allow the front to reach max height. For me, the switch to using low idle and periodically pressing the brake to stay in the compressor on zone longer did allow the front end to go to max height.

i only replaced some of the five Norgrens in the steer compartment, so still might have moisture damaged units elsewhere. And, we have only owned the coach for three years so I have no idea which air bags might be on the coach.

Jerry

[Archived]

Look at the link I provided. There are pictures showing the shape of the bases of the mae west and double flare air bags. Raise your bus, then you should be able to look at your front bag base and see which type you have. Double flare, no bueno. Mae west, muey bueno.

[DON]

That issue of transposed air bag numbers should have been resolved a long time ago and if any of those air bags are out there, installed on coaches that definitely could be an issue with slow or no front lift to or above ride height.

But those air bags are going to be old enough to vote and replacing them would not be a bad idea.

The “Mae Wests” came about because both CC and Marathon were overloading the front axles with their conversion and Prevost came up with that as a solution to raising the front. It did not increase the front axle limits, but it did get nose heavy coaches up in the air faster.

[Archived]

Old enough to vote? Prevost Parts tried to sell me the wrong airbags less than 3 yrs ago, but I new better. Again, here’s the link: LINK

[Mark]

Way back when I was vary active in POG I found out Prevost was reducing the number of different air bags offered. They had a wide variety of different part numbers for various applications such as kneeling seated coaches, motor homes, entertainer, 40 footers and 45 footers. So they did away with a lot of the various part numbers and came up with a few that would work across their product lines.

That was when this mess started and I realized they had switched numbers on their bills of material calling out 630260 air bags when 630259 should have been used. I brought it to Prevost’s attention. Nothing happened. So I started making more noise. Nothing happened. Then I made a lot of noise and the only thing that happened was I really pissed off some Prevost folks.

It all came to a head when we had a rally in OKC, and two Prevost highly placed individuals were there. I had an opportunity to press my case and after some heated discussion the light came on. At that rally they admitted the error and said anyone having issues as a result of a recent air bag replacement, Prevost would correct the problem. I assumed that meant the correct part numbers would be listed where they needed to be listed. Apparently not.

FWIW, this is a direct parallel to the problem Prevost had when they were using blue 350 degree turbo system hoses on the hot side, and the red 500 degree hoses on the cold side of the CAC system. That was also a serious battle, but I gained credibility with one of the guys that were at the OKC rally and he got that glitch resolved also, but it took a long time.

Sometimes big companies just cannot get their act together.

[Dick]

Jerry Does your CC auto-level work as it should when on the aux compressor only?

[Erik]

I really don’t know as I never use it that way. When I park I turn off the engine and flip the auto level switch to level with the aux compressor turned off. The system first levels as it can by letting air out to lower. Then it raises with air in the system. If that is not sufficient it turns on the aux compressor and completes the task. Raising is way slower than lowering. I just let it do it’s thing and most of the time it completes its task in five minutes or less. Sometimes less than a minute if all that is required to level is to let out some air at one or more corners.

when we first got the coach I wy over thought things and did a lot of manual intervention. Now I just flip the switch and let the system do its thing. I do turn the auto level off so don’t know how often it would cycle if left on. I have not used the manual level controls in quite a while.

while parked the bus will gradually sink over the course of several days but it sinks evenly. Every few weeks I start it and let it come to ride height and once there will turn the engine off and relevel as above. Don’t know if this is “proper” technique or not but it works for me.

Jerry

[Dave]

Thanks Jerry. I feel that mine would do the exact same if I had the valves working correctly. Getting on it soon.

[Archived]

To backup Jon’s comments abt Airbag issues, while at prevost winter garden,fl last year they tried to sell me the wrong front and drive bags. I did eventually convincing them what was correct. Only reason for purchasing them here was the price I negotiated . Poor part management. No one at prevost will step up and correct this issue either

.