Hi all, just trying to fix the wifes 08 GL320. I noticed the air inlet tube has a large tear in it, thus bypassing the filter. Also when I bench tested the compressor, it ran when I put 12VDC to it, but when I plugged the outlet hole, the compressor slowed down then stopped?? Is this normal, doesn't seem like it.

Also when I took the metal plate off (held by the 4 Torx screws) i noticed the little metal valves inside were covered with a fine black dust. Again, Im assuming this isnt normal and its crud from not having a filter.

Bad compressor??

 

Probably. Does it trigger a malfunction or warning compressor cooling down?

 

Both.

Ive tried scanning it with my scan tool but I cant read the Airmatic system. I'm just troubleshooting with starting at the compressor.

(Im assuming crud damaged the sealing rings on the compressor piston)

 

What prompted you to test your compressor?

The easiest path is to simply replace the compressor. That may resolve whatever issue you think you have. However, since you seem to be feeling adventurous:

The fine black dust is most likely from the motor brushes wearing, and not related to actual air movement. This by itself could be a point of failure and require a new compressor. Replacing the motor brushes is..... well... not easy, if even possible.

The plastic canister (held in place by the long screws, and pressure fit with a gasket) contains ceramic beads that are intended to remove moisture from incoming air. If your hose was ruptured/disconnected and air bypassed the filter, then you likely have an accumualtion of mositure and possibly dust within the canister. This would impede air flow, affect the performance of your compressor, and potentially push moisture into your valve block (utlimately causing the valve block to fail due to oxidation/rust and sticking valves).

You can remove and wash the ceramic beads, then spread them out in a single layer and dry them for about an hour in a 200 degree oven. Put everything back together with silicone grease on the gasket, and see if that resolves your issue.

Also, the canisters are prone to "cracking under pressure." Quite literally. So there may be a hairline fracture (imperceptable to the eye) that would prevent the compressor from generating the necessary pressure to satisfy the Airmatic requirements. This would also require a replacement compressor.

As for the hose, you can purchase a generic length of hose at your favorite auto parts vendor, on the cheap. Just take a sample of the faulty hose with you so they can match up the interior diameter.

Good luck.

 

Testing is a lot cheaper than just replacing it. I wanted to make sure the compressor really was faulty, instead of blindly replacing it.


I doubt it was graphite dust, as it was inside the compressor area, not the motor side.

I cleaned it the best I could, reassembled the compressor and put it all back together. Ran a "raise" cycle twice, no errors at all, strange. Still getting a new filter and compressor and replacing them as soon as the parts arrive.

 

ACKSHUALLY the hose being ruptured would only let dirty air in. Doesn't have an effect on moisture one way or the other, except to the extent a tiny bit of dried air would have been in the line.

Probably no need to buy replacement hose. I just cut mine a little shorter. It seems to break from flexing from pump vibration, so it breaks right at the inlet.

I don't know for sure, but I suspect the pump has some sort of drying cycle. It heats the beads and then exhausts air through them. The silica beads simply don't hold that much moisture, so they must be regenerated automatically, as you so helpfully described.

Great detailed advice.

 

compressor test is done in the car using star or MB compatible scan tool, under airmatic -> actuations -> pressure test

bench testing really means nothing because you won’t know if it’s able to make 16 bar within 30 seconds or not.

Since you have it out, and you know, it’s suspect, don’t put it back and just swap out a quality good new one. Then go look for leaks in airbags.

 

You didnt say how far your Benz has travelled and if the compressor has been replaced before. If its the original, after 15 years you've done very well. How many miles?

 

Ive replaced the compressor about 3 years ago. Im thinking the dirt made it fail prematurely.

It has about 230,000 kms on it (143,000 miles)

 

If you did not replace it with an AMK compressor, odds are it simply was a junk compressor.

 

It’s not the kms that destroy a compressor it’s the run time in seconds. Also readable with a scanner tool, which gives you an idea of how hard it has been working to inflate your suspension.

 

I understand that... I was responding to Blacks comment on how many miles on the vehicle (at least I thought he/she meant that)

 

Also, the canisters are prone to "cracking under pressure." Quite literally. So there may be a hairline fracture (imperceptable to the eye) that would prevent the compressor from generating the necessary pressure to satisfy the Airmatic requirements. This would also require a replacement compressor.

Yes this is exactly the problem I had. Replacment covers seem to be available at ebay and shipped from China for 20$ but quicker way is to buy a cheap 100+ usd compressor from ebay or go to local junk yard and test your luck. Of buy a used one from ebay as I did, 65 usd for both compressor and solenoid valve body, and my problem was solved. There are plenty available, and even repair kits if your compressor piston ring get worn out.

 

Well its been over a month and its still working perfectly.

I think the reason the compressor wasn't working was, the broken intake line was collapsing when the compressor ran. The line was ripped in half near the compressor inlet. So when the compressor ran, I think the line was "sucked" closed (collapsed) and this caused the compressor not to draw any air in. Thus faulting it out.

I fixed the line, clean the compressor and all has been prefect since.