Was this a sudden fault? Was the a/c cooling weel recently or has it been slowly getting worse?

Have you actually looked at the a/c clutch while someone turns the a/c on and see if it engages at all (no matter how briefly)?

possible causes are fuse, relay, gas in system too low, faulty clutch, fault with a/c speed sensor/belt slipping, wiring, engine temp sensor, etc.

You need to give a bit more info on when and how the change (a/c not working) occured and how the a/c was when it last worked.

__________________
Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32