Q7 2008 air suspension issue
 

Hello everyone, I'm new here.

I write from Dubai where maintenance of Exotic cars is really expensive and quotations go up to the clouds for no reasons when a repair is needed. In the same car I changed the MMI board from HongKong for 55euros when I was asked 5k US$ for the same thing!!!

I have a problem with a q7 2008 with air suspension: the car at one point started to "wistle" or spit out air that lasts 2 seconds, from the compressor body, at the opening of any door even if the engine if off, this whistle continues whenever the compressor is activated too. It seems to be a release valve but I don't understand why it does it when a door is opened.
I've removed the compressor and checked it out, all seems in good order a part from the rusted dryer spring, but I'll probably get a repair kit anyways. Once the cylinder head was off I opened a door and seen that the air was coming out of the crank, from the bottom of the piston.
After reinstalling the compressor the car was squatted down like a lowride and now it doesn't rise.
The compressor now starts and shuts down but the car doesn't rise, I suspect because the air is leaking straight out from the compressor out through a release or high pressure valve. Fact is that I couldn't find a scheme or a section explaining the way this thing works so I can just guess.

I'm not a mechanic, I just want to get the car up on the road again.

At the workshop they say I'll have to replace the full air compressor along with the control valve, (but of course they don't know if the problem will be solved) so before putting the hands deep in the pocket or buying aftermarket parts I would like to know from the community if anyone has an idea about this whistle and the work to be done.