How do you turn on the A/C
 

its a 1991 500sl. Under the hood it says the car has R129 or something a/c. its been converted to that I think. There is no switch that says a/c in the car. is it possible that this car doesnt have a/c?

Almost MB's have automatic climate control. The A/C compressor runs most of the time. If you press the auto button the compressor should should run until the evaporator sensor tells it to shut off. IF you press the EC button the compressor stays off.

The HVAC controls are explained in the owner's manual. If not with the car go to a dealer and order one. MB manuals contain plenty of useful info.