First time poster here. I have a 93 Silverado with a 5.7L. It was converted to 134a about a year ago. The A/c has been working great until today. I was driving with cold air when all of a sudden it started warming up in the cab. Checked under the hood and the clutch on the a/c was not engaged. I tried to bypass it to check the freon but it would not bypass. I put a meter on the bypass (pressure switch) wires and had no voltage to ground. Did a little hunting on the web and found the location of the clutch relay behind the glove box. There were four of them. They are all the same and not knowing which of the four operated the A/C clutch I mixed them around to see if that would get the clutch to engage. It did not and I still had no voltage at the pressure switch. All fuses in the panel were good as well. Can anybody tell me what I'm missing?

Thanks in advance.

 

Did you check the fuse?

 

"All fuses in the panel were good as well"

 

Check the wiring to the clutch for any breaks or frayed insulation. Try and trace it back to the relays. You can also remove the relay and check the contacts in the fuse box for 12 volts.