Hi Matt, thanks a lot for your reply! Hm, at least I got something else to think about - the system is from a '91, but I believe that was the year Mercedes changed from CFC12 to HFC134a? I really have no idea as to what was in it originally, but as far as I know I cannot get CFC12 around here anymore, so I guess I will be running HFC134a.
On the dryer that came with the system, there are two sensors, both of which I was under the impression were pressure switches due to the German wiring diagrams (Both are referred to as 'Druckshalter'). One is set to control the fan and the other one to engage/disengage the compressor like you say. Is there any way to find out whether the pressure switch already present is a low-pressure only, or high/low-pressure switch?
Hm, I might be able to plug one side of the (old and useless) dryer and connect our compressor to the other side - if I'm lucky it should create enough pressure to find out whether it works or not
