wdelcomyn

I have replaced the Airmatic Compressor on my 2004 E500. Also replaced relay. I still have the vehicle up on jack stands. The compressor doesn't want to come on. Does the car need to be on the ground to recognize that it needs to engage the compressor?

I have a good code reader (iCarsoft MB2) and I'm ok with a multi-meter, but I'm not a mechanic by any stretch. When the car was on the ground, the display said "Stop! Car too low", now on jack stands it says "No Malfunction." so that got me wondering. I'd take it off jack stands to check, but with little if any air in suspension, i didn't want to cause damage and also it is very difficult to even get my jack under the car if it doesn't work. I don't have a star tester to run it through its paces. Thanks in advance for help.

kajtek1

Well... I am a mechanic, but your problem sounds like program error.
In normal operation compressor starts every single time you start the motor.
Should go to about 140 psi and wait for next command.
Did you clear the codes?
With SD you should have option to activate the compressor from computer.

wdelcomyn

Thanks Krzysztof. I don't have a star diagnostic. The MB2 can clear codes and I did my best to go through and clear everything. The compressor does not come on with the start of the motor nor at any other time. It is good to know that I don't have to put the car on the ground to test it. I suppose I could try and jump the relay and see if it does anything.

kajtek1

Jumping electronics is never good idea.
Test your relay for operation.
One more tough - you are fooling computer showing the car too high, so maybe dropping it on the ground will do the trick?

wdelcomyn

Thanks Krzysztof. I tested all three relays (the old one, the one I bought separate, and the one that came with the new compressor) and they are normally open and they close when energized with 12V. I tried to test the control voltage coming to the relay and turned the car off and on and never saw voltage. However, I did notice that when I had the relay out, that at one point the airmatic visit workshop came on. I had my wife turn the car on and off a couple times and didn't notice the relay clicking like it was getting energized. I have alldatadiy but haven't been able to figure out if I have found all the fuses. I found one on the drivers side that seems to control the interior suspension switches F37, but I don't know which others control the system. I was just hoping that I knew that putting it on the ground was a requirement.

konigstiger

Front SAM (engine compartment) f45, front prefuse f74 (passenger side footwell).

wdelcomyn

Thanks konigstiger. I think we may have found a winner. Looks like f74 is burned. They are very difficult to get to. the fuses seem to have a catch on them. I'll have to figure out a little tool to push it back so I can pull the fuse.

wdelcomyn

Still no luck. compressor doesn't come on. I jacked up a back tire to simulate load but still no luck. Is there a good manual for trouble shooting a MB 2004 E500? Finding it hard to get good info on ALLDATAdiy, but, I'm sure its just me. I've seen others on here rave about it. Seems odd that there are no alerts on the system with vehicle up in the air and yet the compressor doesn't come on. Also, dumb question, there are two connectors going to the compressor...should they both show 12 V? Thanks.

kajtek1

If anybody got to the bottom of logistics on airmatic, he did not make it public yet
Compressor unit has 2 plugs on it. The big. 40 amp plug is supply power, the other one is dump valve.
I concluded that pressure sensor has to be build into valves on top of the bag.
Bottom line, if the compressor relay is not getting activated with engine start, it has to be program error.

wdelcomyn

I had my wife turn the car on and push airmatic buttons. No voltage at the pump. i've verified that the f74 fuse is good as are the f45 and f37. According to my mb2 scanner, there are no issues while the car is up on jackstands. I don't have any confidence that putting the car back on the ground will trigger the switch to engage compressor. What kind of program error might you be referring to?

kajtek1

Is your scanner allowing you to see airmatic and execute commands?
Like I attached picture of my scanner operating SBC.
Common OBD scanners will read drivetrain codes only, for convenience items you need SD level.

wdelcomyn

I have the iCarsoft MB II scanner. It does have extended visibility into suspension, eps, etc. I can clear codes and it seems like it does have the ability to run through some automated tests. I can't see the picture you posted as it looks like I have to be a member of MB Medic? Lastly, I would hardly call suspension a convenience item

kajtek1

You can drive car without air, can't you?
Use the scanner to start compressor and see what will happen. You also should have option to inflate each corner separately. My friendly technician did it on my car with his SDS

konigstiger

Why did f74 trip. New compressor ok, compressor harness/connection fine, control module damaged. Attachment will give you a better understanding of Airmatic - note pages 20/21/25. Definitive diagnose need to find someone with MB STAR.

cmriv

is your relay okay????

wdelcomyn

Thank you everyone that answered me. Special thanks to konigstiger for the pdf. That's what I had been looking for! So, as mentioned, I replaced the compressor, relay and what appeared to be a burned f74 fuse (more on that in a minute). I had the car on jackstands and the compressor did not kick on. Reluctant to put the car back on the ground because it was such a project to do with my very limited equipment, I started inquiring if it were necessary. Got a little mixed messages there. I was ready to punt. I called a shop in Northwest Arkansas called Shuler Autohaus. The service manager was extremely helpful and verified that the car must have load on the suspension to engage the compressor. So, I put the car on the ground and the compressor came on, and lifted the car and woohoo! I'm in business! Praise the Lord!

So, follow up on F74. I didn't have a direct view of the fuse because of the way the fuse block is mounted. I tried to take a picture with my phone and look at it with an inspection mirror. It looked like it might have a gap. I didn't realize I had a fuse puller, so I attempted to pull that maxi fuse with 90 degree pliers. Needless to say, I boogered up the fuse. The link was definitely destroyed, but I don't know if I did it or not. May have been fine. Didn't smell burned or have soot or carbon as a tell tail sign.

One last note, the service manager at Shuler's mentioned that if the car dropped over the course of two weeks, that it has a leak and should be fixed. Anyone want to comment on that?

Seriously, thank you all for your helpful comments, suggestions and documentation. Very encouraging!

kajtek1

We can dispute endlessly what is acceptable pressure drop, but just for comparison, in commercial truck- air pressure drop 3 psi PER MINUTE still pass
So your suspension rides on about 140 psi and takes 2 weeks to drop.
Can you calculate psi/minute?
I would not worry if it drops in a week.
Dropping overnight would make me worry.

Daniel Clemons

I am having close to the same issue. How did you get fuse F74 out of the fuse block? New pump, new air bags. Worked perfect until one day its below freezing and now even when I push the lift button the pump does not come on. Replaced relay and am now learning about the F74 but cant figure out how to get the fuse out of the prefuse. Thanks!

Daniel Clemons

I got it and it is blown. I believe that air/moisture got in through a crack in the rubber hose and caused the pump to freeze which in turn should be the result for the blown fuse. I hope.

kajtek1

NOW would be good time to service your drier and filter.