I'm attempting to sort out a friends 300 and need some guidance.

The a/c compressor run only after the car is started and then the clutch disengages anywhere between 15-40 seconds. Low-side is 32 and high-side is 150 more or less. The car must be turned off and then restarted for the compressor to engage again.

Even if I bypass the pressure switches on the drier the compressor does the exact same thing. The a/c control panel is brand new and my friend said that the klima "relay" thing is only a few months old.

My guess is that the compressor is bad. But, based on normal compressors I would be able to diagnose it better. With 3 wires going to it, the blue gives 11.8v before it suddenly disappears and the clutch disengages.

Ideas?