[Deleted User]

I don’t know your system but a diode is a one valve. It allows passage in one direction. Therefore if these were installed incorrectly it would have never worked. I find that hard to believe. Without knowing the system I don’t want to speculate, but maybe it was to eliminate backfeeding?

id start with making sure power is getting to all of the selenoids

also remember in 12v D.C. the easiest issue to overlook is a poor ground.

[Archived]

I will do further testing.

The way these look, it does not look like a factory installation and it is possible that at some point in time, somebody worked on the system. Those blue crimps are a hack job…..I don’t even know if the diodes are the correct ones.

I do agree, the Level Low system should not be allowed to backfeed into the CC Auto Level…so the diodes there make sense. If anybody knows that the correct diodes that I should use are, please chime in.

The previous owner had the coach for 4 years and the Auto level never worked for him. We do not know what happened before.

I don’t think signal is getting to the solenoids. I will bypass the diodes and see if I get the solenoids to react. If not the HWH board needs to be checked further.

The Level Low system is working fine in Manual mode. See below the control panel that CC used in this vintage. If I move the switch to Dump, it should open all the solenoids and dump the air. It does not. When I switch to Auto Level ( left side of the switch) nothing happens again.

[Archived]

My guess would be that your auto-level board is dead. To check, measure output voltage on the wires before the diode when you press dump. If there is none the board is dead.

If there is voltage, are the diodes conducting, i.e. cathode towards the solenoids? Voltage after the diode should be 0.7V less if conducting.

I wonder whether the diodes were an attempt to protect the autolevel board from back EMF of the solenoids. Does the autolevel board use relays or semiconductors to switch the solenoids? If they use semiconductors, they would have to be protected with a clamping diode. But a clamping diode would have to go to ground and not be inline.

Gerald

[June]

this is how the board looks like.

[Archived]

I would be concerned that the system would not allow the Prevost level low system to work as intended and would remove or disable it.

The height of the coach is not perceptible from the driver’s seat and if the coach is too high or too low there are consequences that could impact safety.

Does the level low system work as intended and when it is in the driving height mode does the coach go to the height for travel? Too high and the steering geometry changes and the coach can have some handling issues plus the only thing limiting the coach height is the welded rings on the ends of the shock absorbers which means a big bump can do some damage. Conversely if the coach is too low steering is also affected and the turn angle might be limited because the fenders may be limiting the steer axle tires.

[Kirby]

Level Low works as it should. The coach goes to ride height as it should from what I can see.

If I manually lower the coach, then put the Level Low switch in Ride position, start the engine and let it build aux air, it will come to ride height with no problem. I can lower and raise the front and each rear corners with no problem.

I have an Aux system leak that makes the tag dump rather soon after the key is in off position, but as the engine is restarted, it will came back up to ride height.

[Davy]

As long as level low is working my suggestion is to remove the automatic feature.

As to the tag axle dumping air let me half in jest suggest a cheap fix. I know you are a smart guy and can see the partial merit in what I suggest.

Your valves that either maintain the open path between the drive and tag air bags, or lock the air in the drive air bags and exhaust tag axle air bags depending on the accessory system pressure likely coming into the plunger control of the spool. As long as that line is pressurized the valve will not shift to exhaust tag axle air bag air.

So the key is to keep pressure on that line. Lets assume you know for sure that line is leak free. In other words if it is pressurized it is not the cause of your accessory system air loss. If that is a true statement install a solenoid valve in the supply line to the valve actuator. It needs to be a continuous duty normaly closed valve. So when the valve is not powered it is closed, and you maintain pressure to the valve actuator. Tie the valve to a “key on” circuit in the chassis electrical system and any time you run the coach the solenoid valve opens and the system functions as it should as if the valve was not there.

Problem solved with dumping tag axle air. If you have a small air leak at the valve actuator which I would almost bet is the case, insert an air tank in between the solenoid valve and the tag / drive axle three port valve actuator. Of course the bigger the leak the bigger the tank, but what the hell, Harbor Freight sells 80 gallon air tanks.

See what happens when I am allowed to think?

[DON]

Further testing shows that the automatic level and dump CC main board does not send signal to the solenoids. Should see 24v on 3 pins on the P2 connector on the board when Dump is activated and suggested above.

Got a hold of Joe Portelli at HWH and I am sending the board in to see if it can be repaired. Hope they can do it. They only built 7 coaches with that system 27 years ago….it will be something to make this work….

If the board gets fixed then I will revisit the diodes and wiring to make sure there is no backfeeding from Level Low into the Auto CC system…..will post the results of the journey…

On the tag dump, agreed with the suggestion. Certainly a viable work around, but…..talked to Prevost this afternoon and based on the Reverse Tag Logic documentation and my VIN, the retrofit kit for this vintage coach costs a wopping $22…..boils down to just switching air lines on the exixting Norgrens, no additional valves needed, just some fittings. Good time to change those Norgrens since I get the overnight rear lean anyway and they are likely original.

Many thanks to all that provided assistance.

[John]

IMO the $22 fix you discussed w/Prevost isn’t gonna fix much. Jon’s work around would cost about that.

Service Bulletin for Tag Bag Logic

https://secure5.volvo.com/technicalpublications/pdf/Sb96-14B.pdf

https://secure5.volvo.com/technicalpublications/pdf/Sb96-14B.pdf

[Archived]

Well…it is out of the document in the link….

For my VIN, I need kit 141908 and what needs to be done is diagram D 140131…..reverse the airlines in valves 31, 32, 33 and 34…..am I missing something ?

[Archived]

I admit I’m NOT familar with the tag loading system on your vintage of coach. Like yours? my coach(S-5665) has the “reverse” logic tag loading, capable of raising the tag axle and at the same time disabling the tag brakes so as to not flat spot the tires.

I must be missing something??? After looking at D140131, I noticed (a)that there isn’t an INVERSION valve??(b) there isn’t R12 brake relay involvement/plumbing for tag brake disabling when tag is unloaded/raised?? (c) there is a 4th Norgren, most have only 3?? What am I missing??

Can you raise your tag off the grd, or just unload it. And, since there isn’t any R12 involvement, I guess your brakes are still active when your tag is raised/unloaded??

Educate me please?

[Per]

It has been a couple of decades since I looked at the pneumatic system with reverse logic, but I remember clearly from a seminar put on by Prevost around 1991 or 1992 that when tag axles were lifted the brakes for that axle were disabled. I also remeber on my 1987 coach I could not only clear the ground with my tag axle tire, given a few minutes of time my rear would eventually reach normal ride height.

That was not the case with my 97, possibly due to the greater axle weights and the longer overhang at the rear.

[Archived]

I’m very familar with my buses “reverse” logic tag system. Based on the kit# & diagram# that Marius mentioned above, his bus, 90CC, is very different.

Maybe he can unload the tag, but may not be able to raise it or disable its brakes?

Marius? Somebody? Anybody? know for sure what the deal is? Inquiring minds want to know.