Low Air Suspension Issue

[OldForester]

Mike,

I almost called you on this. I agree with you on the schematic. I am putting the coach up on the rack in this repair shop's facility Monday morning so we can change the quick release valve and figure out a way to drain the tank. They think if they can find a fitting somewhere they can put a truck air drain on it that I can drain from one of the access compartments, like the water tank drain. These guys know more about air systems than anyone I've worked with so far. Probably because they're ex-truck and bus mechanics working in a new RV repair facility with big racks to lift motorhomes.

We have also found since my last post that this actuator part number is still in Haldex's system but they have upgraded it to a different part number and it's a two week lead time while they get it made. It's supposed to be cold (down to 27 degrees) mid-week here near Austin, so by changing the air release valve (which sends a signal to the governor on the compressor to unload/load), and making sure we don't have water/oil in the air tank, I will get a chance to test this fix when it's cold. Then if it still doesn't work, we will move on to the actuator, which is not a cheap part, and I will try relying on the extended warranty to help me. So, I will get a chance to change parts one by one, hopefully figure out an air tank drain, and test it before we change the compressor. Because the compressor builds air to 120 psi when it's cold and then drops to 45 psi when the brake's released, as I learned in Van Horn, makes me more skeptical about the compressor. Air gauges are really valuable learning tools!

I'll begin work on a simple schematic and confirm it a little more with what I have and what I learn Monday. Maybe in the next week or so we will have this figured out. At least it gives me something else to do while I'm visiting in-laws (I'm sure others have needed that kind of excuse to work on their coach at certain times, as well.)

[takepride]

Mike and Bill:

While making up your schematic, please figure out what this solenoid/valve does. Twice last December it decided to get stuck and a loud hissing started up. It slowly drained air from the system, though the compressor had no problem keeping up. Fortunately I didn't have far to travel and the compressor didn't have a chance to overheat.

On the second trip, when I arrived at my destination (9.8 miles away), I hit the leveling system and the normal dump valve sound started, as usual, so I know it isn't the dump valve. Several days later, when I returned from my arduous journey, the problem went away, hopefully ne'er to return.

It sits on the aft side of the front firewall, in the same space as the steering box. The two tubes going in and out, both return into the frame rail to parts unknown.

The middle picture is a manifold that is a few inches to the right of the solenoid, but not connected.

[EngineerMike]

Take- looks like a dump valve to me, 12V from the leveling system on either manual dump or auto-level to a gizmo like that dumps my air.
Mine is not on the front bulkhead; its nearer to the coach center, maybe inside of PS frame rail near front air bags w/another near rear.
Could be that on an 03 they used a single dump valve w/lines to the manifold?

[takepride]

eMike:

Hadn't thought of a dump valve just for over-pressure, always thought the spitter did that. When I hit the auto-level button, a different dump valve opens. It sounds like it is a little further back, maybe near front axle. The valve is designed with one pair of 12v wires, two incoming hoses and one outgoing hose connection, though the outgoing one never has had a hose (I hope). It looks evenly patina'ed.

Now, I'm not sure if it just stuck open or if a signal was telling it to remain open. Seems like it would be a common enough part to find at most truck shops. Guess I'll wait for it to die.

One day, if I'm feeling lucky (or depressed), I'll crawl under the coach and have someone hit the dump valve. Then I'll know for sure where it is. At least for a few minutes.....

[Old Scout]

My 03 has two air bag dump valves--front is on inside frame rail p/s, rear is over drive axle. Believe this accounts for the two separate low pressure warning lights on dash--front and rear air. Believe manifolds [front and back] distribute air to bag leveling valves and dump valve. Not sure how lines are run/check valved--cant account for air to horns, dash air guages/buzzer, remote air chuck or parking brake after bags have been dumped [see thread on accidental bumping of yellow release knob].

[takepride]

Thanks OS. Maybe this dump valve is the front one and I was hearing the rear one come on when auto-leveling. Mystery solved?

[EngineerMike]

sounds more to me ike mystery not solved. OS's descr. of known dump valves on the 03 syncs w/my 08 setup, so the mystery valve in your photo is still unaccounted for.
Anybody else got some intel in this air layout?
(posted from my new Kindle, this is cool, & yeah, I'm a geek)

[EngineerMike]

sounds more to me ike mystery not solved. OS's descr. of known dump valves on the 03 syncs w/my 08 setup, so the mystery valve in your photo is still unaccounted for.
Anybody else got some intel in this air layout?
(posted from my new Kindle, this is cool, & yeah, I'm a geek)

[OldForester]

Those are air bag dump valves, tied to the signal to dump air from the HWH panel. I'm currently working the air system with some technicians and I'll try to figure out how they get the signal converted to a dump signal.

There are other places where air is also dumped -- the suspension air drain valve, the quick release valve that controls the parking brake roto chamber (actuator), the air horn, the purge valve at the air dryer, etc. in addition to the air bag dump valves.

[Old Scout]

Breaking news! There are in fact, four air bag dump valves [one for each bag][see picture above] on my 03. The two valves in the rear are connected between the leveling valve and the bag. The front two valves are remotely located from the bags but assume give that all four look exactly alike, they are all dump valves and would operate in the same manner.

"Assuming" the front dump valves work like the rear valves, the dump valves would release air directly from the bags. However, as soon as the bags begin dropping, the bag leveling valves [purely mechanical--no electronics] would sense the drop and begin bleeding the remaining compressed air thru the dump valves to try to re-level the bags [that is, unless the dump valves also act as check valves for the compressed side when dumping]. The idea of an imbedded check valve here is unlikely as I "assume" the "normal" position for the dump valve [not energized] is closed.

Since it has been proven [discussed] that compressed air remains in the system [horn, parking brake, remote air chuck], there must be check valves upstream from the dump and/or leveling valves. This also begs the question as to where the low air pressure guages/buzzers sensors are located so they can sense air pressure --front and rear. There is a multi-port manifold that controls the parking brake actuator but it is not clear how it interacts with the other compressed air components.

[EngineerMike]

OldScout- the low air sensors are (at least on Actia equipped coaches) on the PC board behind the idiot lights. There are two nipples, one for front & one rear if both are "sensed." On Avalanches, which have air brakes, both drive a gauge on the dash. On 04+ Limited coaches there is no gauge, just the low air warning, and only one of the nipples is sensing, the other is empty & the function disabled in the software.

For 03- coaches, I'll have to defer to your more particular experience.

Takepride- do the two lines to your mystery valve enter a Tee which enters the base of the valve?

[Old Scout]

EM--after my under coach inspection yesterday, think we can pretty much agree that the valve pictured above are one of four air bag dump valves. Its difficult to tell on the front valves [mounted remotely from the bags but the rear valves are connected between the bags and leveling valves [one line in from leveling valve and one line out to bag]. The exhaust/dump port on the valve is bare--no hose. A picture is worth 1000 words--wish I had one! Seems the front valves have two nipples and hoses connected while the rear valves had a tee connecting the two hoses to one port on the valves--I think!!

So what was the question again--smile??? Reference my previous post on low suspension pressure and the "stuck" check valves on the compresser/regulator. Its kind of a "chicken Vs egg" conversation but something caused the 175psi relief valve [not the sniffer valve--believe relieve valve is similiar in function to the relief valve on a water heater] on the air drier to literally wear out before the low pressure problem developed with the compressor/air bags.

There may be minor leaks elsewhere in the system but think the root cause here is the compressor/regulator. As I stated before. I was able to restore full air pressure on the 09 by lightly tapping the compressor/regulator housings with a wrench. The diesel engine was still cold so the tapping overcame the conclusion that this problem only occurs with cold engine/cold ambient temps.

My conversation about location of air pressure sensors was off point but was directed toward trying to explain why pressurized air remains in some parts of the system [horns, parking brake, air chuck], after the bags have been dumped.

[OldForester]

I have a number items to discuss on this issue after having the coach worked on by a couple of techs with a lot of heavy truck chassis experience.

First -- the problem finally appears to be fixed! The major fix was the quick release valve on the parking brake. The quick release valve is in line between the parking brake switch and the actuator (called a roto-chamber) that holds the parking brake off. When air is released at the parking brake switch, this release valve actually releases the diaphram in the roto-chamber that holds the brake off the driveshaft. In reverse direction, it applies air to the diaphram in the roto-chamber. It has a port that releases air to the atmosphere when it releases the diaphram. This valve has a spring and seals in it and it is sometimes faulty-either the spring is not strong enough, the seals wear out, it gets moisture or gunk in it, or a combination. One of the clues I told the techs is when it's cold outside (like in the low mid 40's F or less), I can hear a slight hissing sound from up near the differential while the coach is trying to build air. And last week, when in Van Horn, Texas, at 28-30 degrees it took 35 minutes to build up air and this slight hissing was going on all the time. They reasoned the valve wasn't closing fully to allow air to go to the roto chamber, and was partially dumping air until it all got warmed up.

It is a job that takes about 2 hours if you have the right part. They tried an alternative Bendix part and it didn't work so they got a replacement made by a company (I think called Fedco) that is basically a Haldex knock-off or second label, and shares the same Haldex part number. It was an off and on all day job but in the end it worked fine at 72 degrees, as the old one did.

This morning it was 28 degrees outside and I tested it and worked perfectly! Compressor built air to 120 psi, I cycled the parking brake off and on several times and it never dropped below 100 psi, in contrast to the 45 psi before when cold, and this time, no low air suspension warning, which occurs below about 65 psi. I could also feel a much more responsive, firm parking brake switch instead of the "spongy" feel I had before when cold.

The techs also loosened the air lines and took the drain fitting off the bottom of the air tank and blew it out with shop air attached to the air chuck next to the air suspension dump valve. They found very little moisture, but installed a pull-cable drain valve for me to dump the moisture out of the air tank every time I start the coach and have to raise the jacks and air up. The drain valve cost $20, and is commonly used on trucks to drain the tank. The cable was routed out toward the side of the coach. We used a Meritor WABCO valve, part number R12103, which also had a number 478 on the fitting, but there are a number of simple drain valves that can be teed into the bottom air line on the air tank. The advantage of having a drain valve on the air tank is that it's lower than the hose that goes to the air suspension dump valve, so when you drain it, it really gets any moisture remaining in the tank out, where the air suspension dump valve won't get all the moisture out when the pressure is low.

After fighting this issue for 4+ years you can't believe how excited I was to see this work like it was supposed to.

I'm tied up today but will send some pictures later of the old valve and the replacement Haldex version -part #KN28500. The valve cost $45 and new fittings about another $20, plus a net 2 hours of labor.

This quick release valve is located above the driveshaft in the middle of a cross frame rail, near the floor of the coach. I have a picture of its location as well.

Engineer Mike and I are working on the air system schematic and have it fairly well figured out. With the tech's help, we found four dump valve solenoids, one for each air bag. The front ones are above the tie rod on the internal side of each frame rail. The rear ones are on the internal side of each frame rail, near the air bags. They are 12V, as show in earlier posts, appear to receive a signal from the HWH panel, and release air at the solenoid, where they are plumbed into the line to the air bags. I took pictures of each on our coach and can send them in a later post.

I feel like I'm becoming an "expert" on this air system. My coaching would be if you are having air issues, the simple Lowe's/Home Depot air gauge on the air suspension dump valve is invaluable in helping diagnose the issue.

[Gary Arnold]

Bill – Congratulations!

This has been a tough and unique problem to solve. For a long time I thought there must be a problem with the compressor but you proved me wrong.