If you are hot while driving your 616/617 powered 'Benz because your A/C does not work, it is probably because the factory equipped GM R4 compressor is no good. Time to upgrade to a smoother, quieter, more efficient A/C compressor. A Sanden (or equivalent) compressor is the way to go.
Check out these threads:
http://www.peachparts.com/shopforum/diesel-discussion/334249-gen-ii-616-617-sanden-style-c-compressor-mounting-kit-sale-install-inst.html
http://www.peachparts.com/shopforum/diesel-discussion/338192-123-sanden-r134a-vent-temps.html