A/C compressor clutch is not engaging

Oh I see about relay, so it is not something I can change out. I don't think it is low I put gauge on low pressure port and shot up into red. When I squeeze trigger on recharge can pressure on gauge drops to nothing but doesn't seem to be putting any r134 into system. Pressure stays same each time I have tried. That wiring diagram looks confusing for me, I am not that knowledgeable when it comes to that kind of stuff. I guess I can get when of probe tester lights and start poking around. Thanks for help

Yes its a brand new can of 134a. Called A/C pro I believe. Ya but gauge is already in the red when I hook up to low side port, so if it went up then it would be even further in red on gauge, basically maxed out in the red if it did go up when I pulled trigger. But when I pull trigger it drops to 0 pressure according to gauge. The gauge I'm using, the hose and the can 134 are all brand new. I did have a previous hoes engage that I had put on the low port prior to buying the new setup and that also showed the pressure in the red when just the gauge was hooked on. Sounds like I got some kinda issue, expensive probably too with my luck. The serpentine belt and everything looks fine but the clutch will not engage it does turn though when I tried to turn it with the car off. And it turns with a little bit of drag to it l, which from what I think I read is the way it should be, it doesn't spin freely if you know what I mean.