Help! A/C techs!

[L98camino]

1989 K3500 7.4L Silverado.
I replaced the compressor, clutch, orifice tube, dryer/accumulator and all o rings on my truck in preparation for a switch to R134. Took it to my local a/c shop for draw down and charge. After draw down he said that there is no voltage to the clutch. I jumpered the accumulator cycling switch wires and the clutch engaged. The switch showed open so I replaced it. No joy. He is adamant that I should have a high pressure switch on the compressor but the old one and new one donÂ’t have it. Nor can I find a plug that would connect to one. I have seen wiring diagrams the show 1 accumulator cycling switch and others that show the cycling switch and an a/c air inlet valve motor pressure switch. IÂ’m horse trading with him or IÂ’d try a second opinion, which is why I am here lol

Any help would be appreciated,
Thanks, Dan