Thread: Air suspension question

Originally Posted by Maxintosh

I'm guessing a little here, but let me see if we can check the logic of what is going on...

The reservoir fills the air bags, not the compressor directly. The compressor will fill the reservoir when the pressure switch reaches a certain level, and then cut out at a certain higher level, just like workshop air-compressor does.

If the reservoir is holding 'static pressure' then there is no leak in the system, if, however, there is a leak, then the pressure in the reservoir will drop. Leaks could be hoses, seals, holes in bags, loosened nut fittings, or back from the compressor.

To receive the message "Reservoir pressure static when filling" I am assuming that either there is a leak at a comparable rate to that the air-compressor can deliver, or the air compressor is not providing additional air pressure to the reservoir. I.e. most likely that the air-compressor needs a rebuild, or, that an o-ring lets go at a pressure similar to the steady state, so when the pressure rises, the leaks start, but at a lower level, it is not enough to escape.

Anyway thats my 2c worth.

Maxintosh: I have already ordered a new kit for the compressor and will rebuild it when I get home from overseas on 26th June and report further. I just cannot hep but think that there is a gremlin in a pressure sensor somewhere but first things first and then we shall see.
When I was going through the tests that I did today the performance of the compressor did seem adequate but as I said, we shall see.

Originally Posted by uteman

I got a few moments to investigate the car some more today.
Firstly I cleared the fault with the "Faultmate" then did the following whilst car was in driveway.
1. Removed cover from compressor just in case it did not run and I wanted to do further checks.
2. Lift to Off-Road height and back to normal road height and all went OK on several such movements.
3. Lower to the entry/exit level and this went OK but what was interesting was that each time I raised it to normal level the indicating light would stop blinking indicatng that the car had reached the selected height which it clearly had. Then after a few seconds the compressor would start to run again for some time even though the car had already reached road height and the compressor had stopped.
4. This made the Faultmate error reading of "Resevoir pressure static when filling" make some sense as it seems to me that the reservoir was already at pressure but something was giving a signal for it to run again.

Happy to receive any feedback

Either, the compressor is not handling higher pressure which a rebuild will fix
OR, the pressure switch is sticking or stuffed, not reporting change above a certain pressure (top of my list now)
OR there is a leak. You should notice the compressor run as soon as you start up, trying to recover lost pressure when the car is off. Should be easy to rule out/confirm.

There could be a problem with the pressure switch wiring, the ECU may be loosing signal, check the plug, clean and reseat - long shot. I would expect the "Pressure dropping when filling" or Comms error fault in this case (and for a leak).

Think like a computer for a sec, remember we can only 'think' about the code that was fed to us by the original developers. The "[something is wrong] when filling" error is logged because the ECU has instructed the compressor to fill, and [something is wrong] condition has been met while the fill instruction is active. So the "something was giving a signal for it to run again" IS the ECU. For that fault to be logged the ECU must have turned the compressor on - if it didn't you would have "compressor temp rising while not filling" fault.

Originally Posted by bacicat

Tis one shows that it is for the L322. There are others come up from time to time that have a new piston and other stuff, but they are over £100. For the price, if this fixes it - even for a while, you would be ok IMO.

WABCO AIR SUSPENSION COMPRESSOR PISTON RING REPAIR FIX KIT | eBay

Cheers - Gav

BACICAT: After confirming that WABCO do not supply any service items for the compressors I obtained the kit that you told me of through Ebay.
Total cost with postage was something like 29 UK Pounds or 47 Aussie dollars.This compares to $868 plus GST from the local dealer for a replacement compressor.
I removed the compressor and fitted the new piston ring in short time which would be even shorter should I ever do it again.
Result: all seems perfect with the raise to off-road height being much faster than it has been in a long time. No messages coming up on display anymore so all A OK.
Thanks to all who submitted replies and advice and don't hesitate to build your compressor as it simple.