I don't know if the speed sensor was retained to that year, but his car does not have any switches in the AC system. The pressure and temperature senders are transducers which communicate to the pushbutton unit.

Don't disconnect the sending unit. This is unlikely to help.

I think that #7 is the high pressure transducer, just like the E class. Connect a set of gauges to see what kind of pressure you really have on both sides. A non-functioning (closed) expansion valve will give you very high pressure on the high side along with very low pressure on the low side. This will also shut your compressor off very quickly; but it will restart once the pressures stabilize.