Climate control problem - 400e

[rdsc49]

I have a 92 400e. The climate control blows hot air!
I had it in to my MB specialist, and he said the gas was up, but the compressor was not getting any power. I didn't have time to let him tinker, especially at his shop rates. The fuse is ok, but I haven't got much further than that. This thing has more sensors and control modules than the space shuttle. I wondered if anyone has any ideas on things I can look at before taking it in for the inevitable $1000 diagnostic + parts??