Bobbing front end

[Charles Spera]

So I read all I can before testing the solenoids on the manifold. I am having a problem getting the front up high enough to place the stands. I finally dump the tag and the front goes up enough to get the stands in place.
Now I go through all the solenoids and by moving them around I find that the second valve (not the solenoid) is failed or failing. Of course the only spare I have is failed also so I will have to order from Prevost today.
Here's the question(s):
1. I found that all of the solenoids are 12v except #3 which is a 24v version. Can this be correct or has some previous genius mistakenly put in the wrong one?

2. The failed/failing valve will lift the front as long as the compressor is running but when the dryer spits, the front goes down to road level until the compressor kicks on and starts the dance all over again. What's happening here?

Thanks for your input.

[gmcbuffalo]

Chuck I find it unusual that one would be 24 volts. Have you looked at the wiring diagram either in your manual or online?
GregM

[Jon Wehrenberg]

Chuck,

Ignore voltages and the like for the moment and define some things that will help diagnose your problem. First, how much does your front axle weigh and what is the rating on the Prevost axle weights data plate. Let's get past that issue. If you are overloaded on the front axle you may not have a mechanical problem.

But then step by step define for us what you are doing, and the results. It sounds to me that you go to the manual position on your leveling system and attempt to raise the front to its maximum height and that is not happening. With a Liberty you go to the manual position, then switch the front switch to the up position and just wait. If the dryer spits your aux pressure should be at the max pressure and unless it is leaking substantially from somewhere that pressure should be going into the front air bags. Can you provide some additional detail?

FWIW, when the switches are set as I described above you have an open path from the air bags in the front of the coach to the aux air system pressure. So as the aux system pressure goes up or down so will the air bag pressure. I think your issue may not be suspension related as much as aux system related. But tell us more.

[Charles Spera]

Jon,
I think you've nailed it.
I recently replaced the pressure regulator in the aux system. Foolish me, I never paid any attention to setting it, so whatever it came out of the box set at is what it was trying to maintain.
I have now moved the max pressure up and the "bobbing" seems to have been cured.
With my newfound knowledge I would say that the major leak was the pressure regulator trying to drop the pressure.
What is the recommended pressure setting for this regulator?
Thanks again; every day I learn something new.

[Jon Wehrenberg]

Chuck,

Just to put a fine point on this issue keep in mind the pressure regulator has no impact on airing up the air bags when the engine is running. Your aux system pressure with the coach running peaks out at the bus air compressor set point which should be around 120 to 125 PSI.

When the key is off, and the aux compressor is the means by which you maintain aux system pressure it has no impact on your air bags because with the key off the air in the air bags is "locked" in. If you are trying to level the coach solely with the aux air compressor (key on, engine not running) then the aux air system and air bag pressure are going to parallel one another.

As to aux system pressure, I keep mine low, 80 cut out, 40 cut in because all the air operated devices I have in the house work fine at those levels. The lower I go, the easier it is on the compressor.

[truk4u]

I set mine at 60 & 90 for the same reason Jon suggested.

[Danss]

How do you set the different pressures?

[Jon Wehrenberg]

Dan,

I think that depends on the aux air pump and it's pressure switch set up. Some may not be adjustable. Mine uses the equivalent of a well pump pressure switch and a turn of a screw adjusts shut off pressure. Some switches allow you to adjust the pressure differential also.

On some the switch is external, such as on mine, and others the pressure switch is internal to the compressor and likely not adjustable.