Another air suspension problem
 

My e53 has all round air suspension and the problem started with the driver side lower than other side. The compressor was working at this point, but now has stopped.
The rest of the suspension started to sag, so I bridged the relay in the compressor and pumped the suspension back up. since then it's still not going up by it self.
Front suspension went up but rear didn't? I jacked up the car at the rear driver side, and the other rear went up, but both went down when I released the jack.
I can see it could be a few issues, but I don't want to through money at everything, so I am desperate on help on where to start.