No A/C after the fuse box was replaced.

Van lost all power and would not start or turn over. Had a shop diagnose a burnt fuse box relay which melted part of the box so they replaced the entire fuse box. Now everything works except the a/c. I have 12 volts and ground to the a/c fuse, relay and low pressure switch. I have ground to the compressor wire but do not have 12 volts when a/c is turned on. As far as I can tell the dash switch works because the idle is raised when I turn it to a/c. I checked all connections to new fuse box and everything seems to be good. Trying to repair myself cause the shop that repaired it is over an hour away( I broke down on the road ). I had no issues with the a/c before this repair. I tried jumping out the low pressure switch. I connected a gauge to system and it has refrigerant in it. Next I was going to try and bring 12 volts to directly to the compressor to see if the clutch engages. Thank you very much for your time.