Front won't go up or down?

[Jon Wehrenberg]

All of us are still waiting to meet the new Prevost Conversion owner that has no questions. He is either a genius or a fool.

No matter how well you know your coach, no matter how long you have owned it you will still find stuff that was previously unknown. And the newer and more sophisticated the conversion, the more unknowns.

[HarborBus]

OK, here's the latest, it appears that all the solenoids are good. I switched out 1 & 2 and put in 4 & 5 No difference. Additionally with solenoid 1 & 2 in the rear positions I raised and lowered the right and left so I just left it that way. So I guess the only thing left is the valve or valves in one or two position. Would the spool valve have anything to do with that one position (front)?

[Jon Wehrenberg]

Yes. The only valve that appears to be not "shifting" is the three port valve. It should be located on the rear bulkhead of the lower steer compartment.

The valves are simple to work on. Take it out, remove the four screws from the end cap (either one), and carefully take the cap off. My guess is the plunger or the spool is stuck.

[HarborBus]

Everything works............... kinda. I can lower the bus with the switch in the front position and it will raise to ride height in the drive position. BUT, when I put the switch in the front position and lower it I can not raise it at all with the (up) switch. If I raise the tag I can raise the bus any height I want. Prevost says the pressure the tag is putting on the front impedes it's ability to rise. I'm not buying it because if that were the case It should not raise the front it to ride height in the drive position. I'm thinking the #2 valve has a small leak not allowing sufficient air pressure to raise it with the switch in the front position. What does the Brain Trust think?

[Jon Wehrenberg]

Without studying the circuits to refresh my memory I can say this. When you use the road height switch position aux air is directed through the ride height valve that is located top center over your steer wheels. The 5 port Norgren that controls that is "switched" by one of the solenoid valves in the stack located on the rear bulkhead in your lower steer compartment. If your solenoid stack is like mine it is the center solenoid switching the Norgren.

When you are manually attempt to control the height the top two solenoid valves (again, if your set up is like mine) are the controlling valves which shift the five port Norgren to raise the coach. When the command is to lower the front, only the second valve down is used, so check the top solenoid valve. I suggest you check the coil because my guess is the valve is likely OK, but the coil is bad. To verify this either check for an open circuit, or switch coils with one of the bottom coils temporarily.

[truk4u]

Like Jon said, it's one of these bad boys!

IMG_3108_1..JPG

[Jon Wehrenberg]

Elliot,

I presume by your October post you are familiar with the solenoid valves, that they are modular and that you can swap out the parts to eliminate or confirm you have a valve or coil problem.

If you have already gone through the swapping of parts to check operation of the solenoid valves the next step is to verify you are getting power to them. The coil is easy to check because you should have continuity. if you do not, it is bad. But one thing I should point out is that the generic Prevost leveling system may be modified by the converter to provide automatic features. My Liberty has been modified and some coaches have had a converter installed HWH system.

If your bus solenoid valves and coils check OK, then someone familiar with any system mods you may have may be needed to help.

I do believe the advice you were given about the tag is technically correct because when you lift the tag you transfer some front axle weight rearward making less pressure in the air bags required to lift the front, but the person that told you that ignored the fact the ride height valves were functioning so the problem you are dealing with is related to the manual controls. I still guess it is the solenoid valve or coil.

[HarborBus]

Thanks Jon, I'm going to check the coil on position #1 and #2. I did it back on October 27Th (see post #32) but I am more confident now so I'll check them again. I don't think there have been any modifications on my system, there isn't anything automatic about it at all. I bought a new coil and valve when I was at Prevost just so I'll have them. I'm busy watching the Masters Tournament today but I'll get to it tomorrow. Thanks again guys for the impute.

[gmcbuffalo]

Also check the voltage or that there is voltage to the solenoid valve coils. I had a problem at the selector switch, one dirty contact and it would not allow voltage to the coil to function.
Greg

[Jon Wehrenberg]

Elliott,

Since you apparently have no converter installed automatic leveling you should have the unaltered Prevost Level Low system. That will make trouble shooting less complex. I would suggest you just methodically start at #1 solenoid valve and after you replace the coil, or the coil and the valve you check the performance. By doing one thing at a time you will know exactly which component or assembly is the problem.

One thing everyone needs to keep in mind. If the bus ever fails to return to road height on coaches with the 5 solenoid valve assembly, the center valve is the control for all three 5 Port Norgren Valves which in turn routes air through the ride height valves. That is the starting point for diagnosis. That valve is always energized when the key is on and the selector is in the road or driving position. On older coaches with the four solenoid valve assembly I am not sure which one is the driving position valve, but it is important to know.