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Bus would not air up
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Jon,
Thanks for all your advice. We feel that the procedure for raising the coach enough to get under it is too risky for us to attempt given our level of inexperience and the inadequacy of our resources for supporting the coach while we are getting under it.
We are really stuck on one point of logic. As near as we can tell, the ONLY way to control the compressor (i.e. start or stop it from compressing air) is to actuate something in the air compressor cylinder head that allows air to escape from the cylinder on the upstroke, thereby preventing any compression. The manuals we have seem to say that is done by means of the UNLOADER PISTON which is supposed to be lifted by air from the governor when pressure is reached.
We have looked over and over at the connections to the cylinder head, and the ONLY connections we can find are cooling water in, cooling water out, uncompressed air in, and compressed air out. How could the governor in the air dryer control the compressor if it is NOT CONNECTED TO THE COMPRESSOR? If there is a governor somewhere that can control the compressor, how is that possible?
It would great if you can help us get passed this fundamental problem with our understanding of the situation.
Thanks.
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Call Prevost and ask for the name of a reputable repair facility near your location, I think you are being taken advantage of as one with deep pockets.
1-800-387-7386
JIM
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We believe you are correct Jim. We started out by calling Prevost. They gave us the name of three places in Hobbs that might be able to help us: (1) Bruckner Truck Sales. Called them and they said they had no mobile service. We then called the next recommended place (2) Hobbs Diesel. They didn’t even know what a Prevost was. Said all their trucks were out in the oil fields. I asked them to call me back. They never returned my call. The next place recommended was (3) Watson Truck Supply in Hobbs. They didn’t do service calls.
Now I had no recourse but to ask one of the companies recommended by Prevost if there was anyone else in town who might be able to help us. They gave use the name and number for American Equipment in Hobbs. We called them. They came out about 36 hours later. That is now who we are working with. And yes, I believe we are being taken advantage of. We have no other options. We are now having a cram course in Prevost Air Systems using the maintenance manuals & parts manual that came with the coach.
Any additional advice from anyone would be greatly appreciated.
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One other number I carried was Kevin Laughlin, 1-817-271-3124 he always had a good answer.
Bill Jenson will tell you what you have and the theory of operation, but he will not fix it for you.
Bill, 1-800-997-7386.
When your in trouble, call anytime, they will either answer or not!
JIM
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We can try Kevin Laughlin even though he is not the Regional Service Manager for the New Mexico area. He might have a suggestion. We did call James Malcomb, the regional service manager for the New Mexico area. He had no contacts in Hobbs. He did say if we were in Albuquerque then there were several places he could recommend. That did not help us since we are not at all close to Albuquerque.
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I think I might call James back and ask if he can get me to one of these places, even if I had to tow it. Supposedly CoachNet will pay for me to do that if it ever comes to it, but even if it was $1000 it sounds like it would be cheaper than paying these people to experiment with you, and WHO KNOWS what other damage they can cause.
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Prevost has used several different compressor, air dryer, and governor set ups in their coaches.
My two previous had compressor mounted governors, my current one has the air dryer governor. I have not yet dug into my current system to figure out it’s inner workings because so far it is working OK. I would urge at this point that you and your mechanic contact Bendix and or Haldex and get their technical people to assist you. Bill Jensen or Robert Hitt from Prevost are the two guys I would also speak to. If you want to study the technical documents the commercial side of the Prevost Car web site has links to their supplier’s manuals here….
http://prevostparts.volvo.com/technicalpublications/en/manuel.asp
Both you and the mechanic need to be on the phone at the same time so you both can answer questions or ask questions. I am guessing you have the Haldex dryer so you may need to confirm with Prevost how your coach was equipped. I never had the same dryer on any of my 3 coaches.
What I am missing is how the compressor “unloads” when system pressure is satisfied. Why I do not think your compressor has failed is because while its performance might degrade over time, a failure such as a broken rod or a hole in the piston(s) would be evident in the compressor. My guess remains that whatever is “signaling” the compressor to unload and stop pumping is likely the issue.
One of our members had an issue with that and I forget how it was resolved. He also could not build pressure. Maybe if he is reading this he can help.
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GPSMEN,
Here’s some information to help.
This is an unloader rebuild kit for your compressor, just a thought, maybe the spring broke.
This is the standard looking governor, but I realize you may not have this if yours is at the dryer. This governor can be found anywhere that sells truck parts for about 35 bucks.
It seems like the 921 compressor is a standard item, so if that’s the problem, finding one shouldn’t be an issue. If you have a Haldex dryer with integral governor, it may look like this one: Haldex
If you have to be towed, I really hope that doesn’t happen, Stewart Stevens is in Odessa, TX. Long way, 80 miles, but if you get stuck in Hobbs with no help, it’s an option. Hobbs diesel is the Detroit dealer and I realize they blew you off. Maybe a visit in person to explain your problem might get some action.
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Wait Tom I have not had any air problems…YET! HA! I guess this means I have been asking a lot of questions!
OP, am not well versed in the compressor or air system yet so no advice to offer but I do sympathise with you, no fun being stuck somewhere without competant help, at least you are at a campground and not side of the road.
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I would call S&S in Odessa and see if they can help. Even a drive to Odessa would be cheap compared to what these guys are going to charge you.
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Sorry, GPSMEN not G-Man… Too many G’s….. Or I could wait for Gil to correct me!
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Get it going, goober. Geez.
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Thanks to everyone who has commented on air pressure governors. Those comments will likely be very helpful to people who DO have a governor connected to their air compressor, but we do NOT. Our air system is configured in what is called the “blow-thru” mode, and in that mode the compressor is always compressing air as long as the engine is running. The unloader piston in the air compressor cylinder head is not connected to a governor or to anything else (see the photo included with our 06/14/14 1:57:57 p.m. post above). The appearence of the unloader port makes it clear that it has never been used and that the unloader piston always remains in the down (i.e. loaded) position.
Therefore, since we had no air coming out of the compressor when the mechanic disconnected the output hose and since the compressor is configured so as to always supply compression when the engine is running, we had to conclude that something in the compressor has failed. We believe our governor is integrated into our Haldex DRYest air dryer and it serves only to make sure excess air is exhausted when the set point pressure is reached. That governor does NOT connect to the compressor to unload it.
I hope this information will be helpful to those who may have a configuration such as ours. We were at first baffled when we identified the attachment point on the cylinder head for a governor and saw that nothing was connected there.
We discovered that our air compressor, the Bendix BA921, is very hard to get. It is obsolete and not manufactured anymore. All that is available are remanufactured air compressors. The part number is R23535534. We may have one arriving by overnight delivery tomorrow, and if that turns out not to be the case we have located one in stock somewhere else as a backup. With some luck we may finally get our problem resolved, and be back on the road by Wednesday. One week after we arrived here in Hobbs and discovered a problem.
A call to Bill Jenson was very helpful to us in figuring out what equipment we actually have in our coach.
GPSMEN
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Excellent explaination. Now I am really curious as to what suddenly happened to the compressor to make it stop pumping air. Expecially if it was not evident with the compressor off the coach.
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Here’s a rebuild on e-bay for 4950.
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