One of the most common reasons for the compressor not engaging is loss of
refrigerant (freon). The sensor switch for that is right behind the left
high beam headlight, forward of the compressor. The switch should be closed
just sitting there. If you don't have an ohmmeter handy, you can also start
the engine and turn on the A/C full cold; momentarily shorting across the
contacts in the connector will engage the compressor if loss of refrigerant
is your problem. Don't run the compressor more than a moment that way.

There is also a relay, which the Helm manual indicates is the front one on
the driver's side of the engine compartment, almost hidden by the washer
fluid reservoir.

Sadly, '93 was the last year of using R-12. If the system has been converted
to R-134a there will be stickers under the hood. If not, and you need a
charge, you will probably find the cost of refilling with R-12 to be more
than conversion to R-134a... especially since there must be a leak if the
refrigerant is gone.

Mike