kajtek1

Big credits to fellow MB owner from Finland handle valotus for sharing his experience and to Kirbie Engineering Solutions (ebay) for manufacturing parts not supplied by MB.
My wagon has front struts, so it is not full airmatic, but compressor is the same.
Occasionally while having heavy load I would get the error with white arrow pointing up and message to visit workshop.
Gathering the info from the net, I concluded the compressor wear out and even it pump suspension on empty wagon just fine, under the load does not build enough pressure. So here is what I did.
Picture showing parts for service and compressor access after inner fender and belly pan removal.

kajtek1

When compressor rebuild is explained on Kirbie video, I check the dryer.
The car was in NY for few years and not showing corrosion outside, the internal parts of compressor had advanced corrosion, but 3 last years in California. We are at the end of very long and very dry season.
The so-called dryer was dump wet. The granules were soaked. Meaning in the application it was actually humidifier.
So 1 hr at convection oven @250F made the granules bone dry.

kajtek1

Next comes air filter.
This is in-line filter design for fluids that MB is using for air.
The design puts the filter in reverse to the arrow showing on the filter itself. I think this is bad engineering as the cartridge inside was rattling and air flow in reverse move it from the neck allowing the air to bypass the filtering cartridge.
Even I did not see mechanical dirt inside the filter, it would not let the water thru and the dryer pads did show black dirt, that bypassed the filter.

kajtek1

Lastly my personal touch.
I don't like the idea that compressor is wearing out and I am not aware about it. So I add a Tee on the air line and extend it into the cabin with pressure gauge for monitoring how often the compressor comes up and how fast it build the pressure.
That will give me some time to notice decreasing performance.
Will observe the pressure and report here after some driving.
Did not want to make the installation too permanent, so no hole in firewall, just tubing hiding behind moldings and body parts.

kajtek1

Did some driving with pressure gauge in the cabin, before I put it to rest in engine compartment...... just in case I would have to check the system in the future.
Here are my observations how the compressor engage.
-each time the engine starts, in 1-2 seconds the pressure jumps to 130-140psi, what I take as self-checking feature.
-the pressure will drop to 80 psi in few minutes and when you stop the car, it will go down to 0 in about 1 hr. I don't know if that was factory design, or old check valves leak.
- our wagon holds the air for couple of days, so had only 2 times time to observe how the system inflate.
The pressure jumps to 160 psi, what looks like cut-off for the compressor and then within couple of seconds drops - to jump again.
That can last for couple of minutes, so my conclusion is that with new ring compressor is giving way more air than the 4mm tubings and valves can transfer to the airbags, therefore the pressure fluctuation.
Now I have easy way to find if the red "visit workshop" comes from compressor failure, or suspension failure.
Also I can remove the gauge and install inflating valve.
Still don't know if/how it would work with computer control and hope I will never have to find out.

kajtek1

2 months later I drove the car for some distance including 1500 miles with 4 passenger and luggage.
Did not park in freezing temperatures, but had the car at 20F.
The white warning message that was showing on occasions for last 2 years never come back, so the above rebuild definitely fixed it.

kajtek1

Another update.
Few months later the troubles with suspension come back.
Having the pressure gauge I was able to troubleshoot and determinate that compressor pumps almost 200 psi just fine, but longer search found that my air tubing had a pinhole right above rear axle.
Hard to see and it opened only under high pressure. Probably would never find it without option of disconnecting the pressure gauge and hooking up garage compressor to it.
Now my system holds 120 psi overnight.

MACEDON

Thank you for this post

kajtek1

New members ask for the pressure gauge installation, so one more idea is to access main tubing under rear seat if all you want to do is adding a gauge.
I discover that under the fact.
In the mean time I sold the wagon, so no longer own air suspension. Fact is that missed it. The 2008 sedan on 16" wheels gives me boaty feeling, when lower profile wheels on other MB make potholes rattling your teeth.