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Level Low mystery
1988 XL40 Liberty Coach. Level Low with the 4 port manifold. Just got this coach, guy tells me that the suspenion only works when you go to “Road”. Stopped working in the front all together.
Order new 3 way valve from Prevost. Swap the coil, its good. 3 way valve clicks, but wont pass air. Originally, the valve had pressure into port 3, port 2 feeds the 5 port, and port 1 was exhaust. It wouldnt do a damn thing. Have voltage at the coil, coil clicks. Swap coils, same result. So I actually have 3 of these valves brand new, swap for a different one, same result. I can dump the front because by default the 3 way is set to exhaust port 2 to 3. Verified the 5 way and everything after is working by putting air to the 5 way, functions as it should.
For the hell of it, I decide to switch the ports on the 3 way valve. Put pressure to port 1, and let port 3 exhaust. The valve actually functions this way, but as expected commands are opposite. Down is up, up is down. Since this 3 way is solenoid activated it occured to me that maybe the spool needs to be swapped around the opposite direction?
Has anyone every had any experience with this issue? If your coach has the 4 port manifold and the 3 way solenoid activated front valve feeding the 5 way air activated valve, can you take a picture so I can see what ports are going where?
Any input is appreciated!
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3 Replies
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The very first thing anyone should do before starting to swap around parts or connections on any coach pneumatic system is to pull up the pneumatic diagram for the coach from the Prevost web site, starting here:
https://secureus5.volvo.com/technicalpublications/en/manuel.asp
If needed copy the PDF file and bring it to a print shop like Kinkos and get it blown up because the detail is easier to read. A 1988 coach would have sirens and warning bells going off in my brain for several reasons, primarily the possibility that a previous owner or his technician may have tried to get creative and started making changes, or that a coach that has not been maintained now might have a system that is water logged or corroded internally and parts are not functioning as intended. Any time I have been confronted with problems in the level low that do not make sense I try to follow the electric signals to the respective valves, then verify the air that is supposed to flow as a result is in fact flowing, and that the part receiving the air signal (or electric signal) is indeed shifting and flowing air as intended. That is a long cumbersome process but it always turns up where the problem lies. But the diagram of the system is essential to following the paths.
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well, got it working. My problem was assuming that it had worked before. Swapped the spring and solenoid to opposite sides of the valve, switched the pressure line to port 1 instead of 3, and now it works perfectly. I’m still not 100% sure what the deal is. My thought is that I shouldn’t have to ever take apart a brand new valve and move things around on it. But then, I also don’t understand why liberty coach would take a 24 volt system and thrown in some 12v solenoids. None of the diagrams I was finding showed exactly what lines went to what ports on this bus. I have all of the books and manuals on it from prevost and liberty coach, and the suspension seems to be an area that is lacking detailed information. Ideally it would say something like the 3 port valve is fed from the aux air tank to port 1, port 3 is left for exhaust, and port 2 feeds port 4 on the 5 port valve. But nope. Just shows lines running to valves. The other interesting thing is the 3 port valve by default is set to exhaust open (no power) with power, it changes to pressure open. The charge air coming to the solenoid is what is used for the valve to push the piston against the spring and allow the pressure to pass through the valve. The way it was sent to me by norgren, it wouldn’t use pressure from port 3 to open the valve, and switching pressure to port 1 simply made the valve work in the reverse as expected. anyways, it works, and I have 3 extra valves now. I’m still going to continue researching how this was intended to work on this coach. I may actually switch this to a 5 port manifold with all air actuated valves and eliminate this 1 solenoid activated 3 way.
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The solenoid actuated valves are exclusive to Liberty in your vintage all the way up to today’s production. It is how Liberty has designed their automatic leveling feature.
Generally speaking Norgren valves have a neat feature most are unaware of. I am speaking solely of the pneumatically operated valves. If you apply pilot pressure to port 12 you push the internal spool to open the path to ports 1 and 2. Remove the pressure and the path to 1 and 2 is closed. For me that is an easy way to understand what is happening within the system when I follow air pressure.
The 12 and 24 volt issue is likely because your coach is a 12 volt coach. Liberty installed components will be powered by 12 volt, while Prevost installed components will be powered by the chassis 24 volt system. We see that situation on later model Classic coaches which are 12 volts, and we see all 24 volt solenoids on the Elegant Lady coaches because on those the Liberty conversion is 24 volts.
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