Volvo Repair: AC, o rings, pressure switch

Question
I own a 740GL 1988, car runs great 258k miles on engine & tranny no problems. I rescently did some restoration and allowed the auto to sit up for some time. I descided to change the freon system from R22 to R134, changed seals and O-rings. Compressor does not want to engage, is there a difference in PSI that I missed or a relay (besides under dash) that needs to be changed, I do not feel clutch is gone because it moves freely.

Answer
pressure may be a little higher but close to the same may be 10 psi higher.you will need tofault trace the electrical system  check for power to the compressor then in and out of the pressure switch on the acumulator the large silver canister near the firewall.