generally, if the pressure is too low or there is moisture or air in the system the compressor will not turn on. i would get it professionally vacuumed out and have a new canister put on. if the canister has ever been exposed to air or it has been depressurized for any amount of time, it needs to be replaced. the canister is what absorbs any moisture. after almost 20 years, i would replace it regardless.
when you take your pressure reading, make sure the car is running and the compressor is on. it should be about 35-40 psi. with the compressor off it should jump up pretty high. if it was charged with the compressor off, im guessing that it is low on freon or air is trapped in the system.
6000k headlights, LED license plate fog lights, tinted taillights and to top it all off, 2 12" air horns!
the gf:'00impy 3.8, every option. COTM July 2013