OK, I got the new AC compressor on, my vacuum pump had problems so I took the car to a competent shop whom I know, but they are not exactly Mercedes specialists. It held a vacuum well, but the compressor clutch will not energize so they are at a standstill for charging the gas. I'll stop by and see what I can see. Any suggestions? All I know to check is (1) single wire which plugs on at the clutch; (2) two control (pressure) switches at receiver drier: one controls clutch in case of high/low pressure, one controls aux fan, correct? Maybe a wire is loose.