I don't have an A/C machine at home but I do have a set of gauges.
How can I pressure test the A/C system at home without buying lots of cans of A/C dye?

I was playing with the Imperial tonight. I flushed the heater core with water and it leaks. Yay. Finding another one will be fun.
Just for giggles, I pulled the cap off the A/C schrader valve. There was a bit of residual pressure in the system. Not much mind you, but there was positive pressure.
I spun the clutch by hand and the compressor seems to turn smoothly. I can't feel any appreciable resistance but there's hardly any pressure in the system.
I fired up the engine and jumped the compressor clutch. It kicked in without any bad sounds. There was no change in idle speed but I wouldn't expect that after turning it by hand.

I'd like to push my dumb luck and see if the mechanical bits of the system will work.

What's the best way to pressure test it at home?