W639 air suspension basics troubleshoot etc.

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ObusVenter

New Member
Joined
Jun 1, 2021
Messages
4
Location
Whanganui New Zealand
Car
2008 V350 (Viano W639)
Hi all. Thanks for having me.
I have a 2008 V350. It is a Japanese import into New Zealand of the Viano LWB, with a 3.5 petrol V6. Right hand drive. I realized today it has been weeks since I heard the air height compressor adjust the ride height.

There are plenty of air suspension discussions but I can't find anything specific to the W639. The symptoms are that it is as dead as a doornail. No warning messages at all. Also, the height adjustment button and air suspension locking doesn't seem to have power. That is all I know sofar. Plus the fuse under the bonnet is intact.

Can you guys please give me a step by step walkthrough of diagnosing it? More importantly where are the various components and circuits?
 
It was rare I would hear mine operating, how are you sure it's faulty, is it sat low?

To operate at the rear we need to press the LED button for a couple of seconds till the LED changes state.
I then rest my leg on the rear bumper, press the down button, and I feel it drop slowly.
As the wheels start to turn again the dash warning come up as low until it corrects itself. I could do that on the rear buttons but never bothered.

Otherwise I would suggest a Star diagnostic session to see what that tells you.
 
Thanks for replying.

I noticed it rode lower than usual. That was when I realized that it must have been weeks since I heard it. At least there doesn't seem to be a leak.

Faint whirring was audiable with the pump activated. Also when parked in the garage you could hear the solenoids making a faint klicking as the ride height drop. Buttons are dead doesn't matter how long I press them.
 
I am struggling to find the relay for the compressor. Anyone have an idea where they usually are?
Also, on the fuse box diagram there is something called "secondary air pump". Is that AC related, or could it be the suspension compressor pump?
 
Hi onus I have the same problem with my viano did you manage to sort it out ? I can’t seem to find any electrical information
 
No problem Mark. Been called a lot worse...

Had it at my local mechanic, who has some experience with Mercs. There was a thermal cut out error on it. He tested, re-tested. And basically couldn't find anything wrong. It simply refused to work.

So he did a reboot, by disconnecting and reconnecting the battery. I'm not sure if he did a hard wire reset (touching the + - battery cables for 30 seconds that would discourage all the little electricery stuff). But when he reconnected everything was working as it should.

I expect this to not be the last I heard of it....
 

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