From my experience on my 93 there is a switch at the evaporator core as well as a switch at the condenser. I did a full flush and cleaning of my system and full o-ring kit when I retrofitted to 134a refrigerant.
Do you have an automatic or manual trans? There is a safety relay on vehicles with an auto trans that could fail and not let the system kick on. This relay is located in a little rubber case on the outside of the evaporator core but the glovebox has to be removed.