Power to A/C compressor

[Raindoc]

Just bought a 72 Blazer w/a/c. I had one 27 years ago when I was in college. I am trying to work out some wiring issues,#1 getting the air to operate. Question: can someone walk me through the switch(s), relays,sensors etc that carry power from the controls omn the dash to the compressor clutch? Mine had an aftermarket switch that sent power to the compressor but I want it like it should be. What postion on the control panel activates the compressor? I can not identify a switch unless the fan switch has a position that does it. One of the wires leaving the fan switch activates a relay located under the glove box but my fan switch is bad so I cannot test it-yet. Does that relay control the compressor? Also is there a good wiring diagram for 72 Blazer available? Thanks and I really apriciate this forum.