1995 Other Mazda Models Air conditioning compressor not enga

When I turn the AC on, the compressor does not engage. The blower fan kicks on fine but there isn't even a click of the clutch activating. I checked the fuse under the dash and it is fine. Other than that, I can't find any info on what else to check. I don't know what voltage I should get where - it appears there is only 1 wire going into the compressor. I hear of pressure switches and such but have no idea where to look for them or how to test them. The manual I bought is no help at all. It says I shouldn't work on any of it. Well, maybe not the compressor but this stuff should be simple enough.

It worked last fall but in November the harmonic balancer fell off and pinned itself between the frame and the crankshaft causing the car to - um - die. I got that fixed and haven't ran the AC since. I don't know if there was extra damage, or if the mechanic didn't plug something in right. Maybe it's just a wire. Maybe I need a new clutch. Or the whole compressor. How am I to tell? Donation is on it's way!