Mercedes: A/C compresspor, r 134a, shaft seals

Question
My 1989 300E a/c compressor doesn't engage when a/c is turned on-what do I do?

Answer
Edgar,
Compressor clutch is controlled by a magnetic switch internal to the pulley. It might be a fuse, but the compressor has a low pressure switch to keep it from self destructing when the refrigerant get slow, as that is the carrier for lubrication also.
I would find an independent auto AC service and have the freon checked. It is not uncommon for a vehicle of this age to loss a certain portion of freon over time by the shaft seals.
In any event, with the price of feon12 at about 40.00 per pound it is important and required by law to locate the leak  during servicing.
If an R 134A conversion has been done, then you could get one of the die kits at Napa, or Auto Zone and do it yourself if your mechanically inclined.
Good Luck and let us know what you find out.
Rob