1997 Chevy Silverado AC question

My a/c is not working. I've bought a re-charge kit and after reading the directions and hooking it up. It shows I may have some mechanical problems. My compressor clutch is engaged when the a/c is set at high and the engine is at idle. It shows the pressure as off the charts high when hooking up the re-charge kit as well. When the compressor clutch engages it makes a loud continuous rattling sound. What's the problem??