Did you turn the refrigerant can upside down? That will inject liquid which will seize the compressor.
Nope. It was one with the trigger on it and a gauge, and I just hooked it up and got the reading. The main reason I was checking it out, is that on the drive home, the belt started squealing worse than it had been. I knew something was wrong, but wasn't quite sure what. I figured it was the clutch, but when the compressor was removed, it was locked up tight.