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Old 10-27-2018, 12:18 PM   #1
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Air bag pressure getting lower and air horn not working

Noticed over the last few months that my normal airbag pressure is dropping. 6 months ago it would hover at around 70psi while cruising down the hwy. Now it hovers around 50psi. I know that the airbags aren't leaking since the pressure gauge reading air bag pressure holds air over night at the same pressure it was at when the engine is shut down. Not an electric gauge since an air line goes directly to it. If I lift the rear with the leveling jacks it does release the air pressure as it should. The compressor seems to run all the time as well and the storage tank empties rather quickly. I'm going to begin the diagnostics process on Wed since it's my day off. No hurry to get it fixed. Just needing to diagnose it so I can prepare for the repair.



Here's what I'm planning to do. First off I'm going to plumb in an air gauge right after what looks like a check valve on the compressor outlet by teeing into the air line. I'll add a air chuck port and shut off valve to be able to fill the system using my shop air compressor. Plan to pressurize the system to around 100psi and see if it holds air. If so, I'm assuming that the problem is with the compressor. If not, than I'll be listening and spraying soap to try to find any leaks. I will run the compressor and see what pressure I achieve using it instead of the shop compressor. I believe that it is the original air compressor.



Does this sound like a viable method for finding the problem? Any other suggestions would be helpful.


If I do have to replace the old compressor I'm looking at the Viair model 485C. It's a newer model that's supposed to be 100% duty cycle @ 200psi capable. Figure I'd rather have more capability than less. Any opinions?


I've owned this baby for 9 years and am now getting inspired to fix any and all known issues.
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Old 10-27-2018, 12:59 PM   #2
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When asking for help; it would help us if we knew what vehicle year and model you have.

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Old 10-27-2018, 01:08 PM   #3
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Sorry, forgot that...


1992 AS Land Yacht 36' motorhome with TAG axle. Updated my profile so it will be always available and visable.
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Old 10-29-2018, 07:18 AM   #4
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I guess this forum has lost a lot of its helpful support people. I can't imagine that nobody here has faced diagnosing, repairing and upgrading their air bag system. Too bad since I was really looking for some feedback.
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Old 10-29-2018, 10:09 AM   #5
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Originally Posted by jt240z View Post
I guess this forum has lost a lot of its helpful support people. I can't imagine that nobody here has faced diagnosing, repairing and upgrading their air bag system. Too bad since I was really looking for some feedback.
There are periods throughout the year where many members are busy with other things and don't have or take the time to read the forums. There's still a lot of helpful support, sometimes it just takes time for them to catch up.

What you're planning to do should work. Don't be surprised if the leak is in the check valve. All it takes is for a small speck of dirt or similar to keep the flapper from closing which would allow the air to escape back through the compressor. I doubt very much the compressor is the problem, that's what the check valve is for.

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Old 10-29-2018, 10:31 AM   #6
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Anyone know for sure where the check valve is? I see something that looks like a check valve on the output of the compressor but I've read other posts that say it's at the reserve tank inlet port. Those that have said that though had 310/345 classics.



I wish that AS had better schematics of the vacuum and pneumatic systems in the owner's manual. AS doesn't seem to have documentation for the earlier models. Seems like the older paper system was never converted into digital documentation.



I guess that's what makes forums like this so critical.
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Old 10-29-2018, 11:03 AM   #7
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I have seen the check valve located in different spots depending on the year, model, and what previous owners have done to the system. I found one inline on the Supply air tube between the compressor and the tank. You'll just have to investigate your system. It is common to have one right at the compressor like you describe. They are cheap to buy so replacing it is a good place to start I think. I wonder if there might be a problem with your pressure switch also. I believe that they are 85/110 +- from the factory.

Many of us have replaced our compressor, wiring, and controls. I would suggest that if you do replace the compressor, that you replace the relay/pressure switch with the Viair 85/100 combo switch or something similar. Ive had very good luck with mine anyway. I would also power the compressor by running a direct wire (8ga or larger) to the battery with an inline fuse of some sort. Then the existing factory wire will act only as a switch wire to the relay. The factory wiring is undersized. That's my opinion.
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Old 10-29-2018, 11:19 AM   #8
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Thanks for the reply Mayco. Already changed out the wiring to go directly to the battery. The problem I'm seeing is low air pressure in the system and the pump never turns off. The most I've been able to build is around 50psi. The compressor has run for several hours straight so I'm sure it's taken a beating over the years. I'll be doing some testing on the system tomorrow. That should give me a good direction. If the check valve is bad and not easily accessible I may just add one after the compressor outlet. Never hear any sign of leaking air so I don't think it's a bad connector or leaking line.


Already purchased the very same Viair pressure switch you described. If the compressor does turn out to be weak, I'll be picking up a new compressor. What do you think of the one I posted a link to above. I know it's a little overkill but I figure, if it can work at 100% duty cycle @ 200psi, than it will be very happy at under 150psi. It's a little more than the lower psi units but I figure it's piece of mind.
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Old 10-29-2018, 11:48 AM   #9
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I think it's a real good choice in a compressor. Especially if you add a quick coupler for an air hose for filling tires and what not.

If your compressor is running continuously and you're not building pressure it sounds to me that the compressor cylinder innards are worn out and not sealing..or rings..I'd replace it.
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Old 10-29-2018, 12:11 PM   #10
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I'll start the diagnostics process tomorrow. I'll post the results once I have them. If I do end up needing a new compressor, I found the Viair 485C single compressor kit for $253.47 with free shipping from a Viair authorized reseller on eBay. That's the best price I could find for that model.



The MH already has an air chuck port but it's never been usable since I've owned the MH. The chuck is corroded and the air pressure is too low to properly inflate the tires. Need to achieve 100psi minimum for that.
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Old 10-29-2018, 01:16 PM   #11
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Check out the compressor Tony (Isuzusweet) installed in his 310. I think it's in his Mistress thread.
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Old 10-29-2018, 02:11 PM   #12
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Ya, I looked into the ARB compressors but decided that the Viair was easier to find and had a better potential to find needed parts if something went wrong. I could get a dual compressor (two individual compressors) system and have a spare. The dual systems usually run for about a 1/3rd more money but has all the parts in the single times two. That way I'd have a drop in replacement if something went wrong. I could also set up the two systems for different terminal pressures. One system for the air bags while the other for tire inflation. I could easily stow the second system in a lower or rear compartment.
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Old 10-29-2018, 02:54 PM   #13
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I'm not sure if the Land Yacht is the same as the Classic but some general observations. You say your air bag pressure is dropping. Where are you measuring that pressure? You can measure at the tank or as my coach is set up, measure what is actually in the air spring.

From your comments and those of others I'm going to guess your compressor is failing. The sure way to tell is to remove or isolate it from the system and measure pressure directly at its output. If it fails you have your answer. If it makes pressure, follow the system isolating components as you go.


The Viair are great pumps. I installed a 480C many years ago with no problems since. Your compressor has made it more than 25 years so I wouldn't worry about double compressor setups, put a good unit in now and it will probably out live you.
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Old 10-29-2018, 03:44 PM   #14
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Quote:
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I'm not sure if the Land Yacht is the same as the Classic but some general observations. You say your air bag pressure is dropping. Where are you measuring that pressure? You can measure at the tank or as my coach is set up, measure what is actually in the air spring.

The system gauge shows actual pressure at the airbags. As the MH moves down the road you can see the pressure jump up and down as you hit bumps. I'll have a gauge on the tank pressure tomorrow.
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Old 10-29-2018, 07:43 PM   #15
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Put the gauge directly on the compressor output first to check it out. It might save you a lot of time digging into the rest of the system. Is your coach on a P-30 chassis or something else?
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Old 10-30-2018, 09:42 AM   #16
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My coach is based on the P30 with a TAG axle.


Started the diagnostics today. I pressurized the system to 130psi using my shop compressor and found my first problem. The service air chuck on the side is leaking. Couldn't hear it over the noise of the engine running and the compressor pumping but was easy to locate with the system pressurized and nothing running.



With the system fully pressurized, the air bags are holding height and pressure at 95psi. Did verify that the inside pressure gauge maintains pressure reading even when the air tank is empty so this does confirm that the gauge is actually reading the pressure inside the air bag and not the system pressure. I'll check to see what the compressor can put out but I'm pretty sure I'll still replace it since it's 26 years old and there's a fair amount of corrosion around the fittings. Newer compressors are more efficient and higher volume as well.
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Old 10-30-2018, 10:40 AM   #17
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Well that was easy! Good job
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Old 10-30-2018, 10:59 AM   #18
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Not done yet. Found the check valve to be defective as well.
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Old 11-02-2018, 10:20 AM   #19
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Saga continues. I ordered a Viair check valve that should arrive some time today. I did replace the leaking air chuck and ran the compressor without the check valve. The original compressor was able to pump the system up to 105 psi and than it shut down the compressor. That's something that hasn't happened for some time now so glad that the compressor looks to be in working order.



I still have a small leak in the system that needs to be addressed. If I pressurize the system it only holds pressure for about an hour before it's back down to 0 psi in the reserve tank. Air bag pressure remains constant though. That's with a cutoff valve in place of the check valve. I pressurize the system using the house compressor and isolated the system with the cutoff valve. The compressor is completely disconnected so no back bleeding through that. The problem is I can't hear any leaks. Not that my hearing is as good as it should be.



Once I get the check valve installed I'll start trying to find the remaining leak. My approach will be to isolate components in the system from the air valve back toward the compressor and see where the leak is originating. First step will be to make sure the air isn't bleeding down through the air horn solenoid since it's easy to isolate without crawling under the coach.



I've picked up 50' of 1/4" DOT air brake line and some 1/4" NPT to air line push-to-connect fittings. I'll start by cutting off air to the leveling valve. If it holds pressure than I know it's around the leveling valve. If not, than it's something associated with the air tank. I know it's not between the leveling valve and the air bags because the bags hold pressure over night with no problem.


If it does turn out to be the air valve, does anyone know of a good source to pick one up? How to identify the one that's currently installed? Best way to replace it? I think I only have one air valve on the curb side that controls both TAG axle air bags.
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Old 11-02-2018, 01:26 PM   #20
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If you use the blue box search function on the top of this page it will bring up many threads on the air valve. I punched in "Motorhome suspension air valve" and got a page worth of hits from Airforums

Here is just one that is specific to the LY

http://www.airforums.com/forums/f312...elp-72228.html
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