i'm fighting something similar. if i hotwire to the compressor everything works great. can't get the compressor to come on when wired to the car.

i have been working off the wiring diagram

http://f1.grp.yahoofs.com/v1/oNpcRvlSIidZsb-CuDN5-kIWmjk2KZ5eLGvnS6gmauZoNrr-XwgZ3C6-PxXLMtvM2xdEiLyMxTwn78JDoLlV-Xe3DKJ88ZjF/hvac%20wiring%2083%20benz%20300d.doc

if you can't open pm me and i'll send it to you. where is the relay for the ac compressor?

pat