a/c compressor not starting

Just installed a different radio/cd player in wife's '98 Safari. Not a difficult task. Problem is that now the a/c compressor is not engaging. Have had the fuses checked. All ok. What do I look for now? Does the troublesome brittle vacuum line come into play? All the controls are working-vent, defrost, floor, etc. But not the a/c. Have noticed interior lights dim slightly when dash switch is placed in a/c position. Was told to tap lightly on switch at condensor, that 99 percent of the time this is the problem. Tapping didn't help. Taking a paper clip and jumping the switch did. The compressor kicked in. It is now apparent that the low pressure switch on the accumulator is the problem. It is a dealer item only, on models later that 1993. Live and learn........