OK. Now I'm a bit worried. I connected the can to the low side... switched the AC on, and proceeded to charge the system. The needle on the gauge read into the OK area as I was charging the system but when I let off the button on the can, it read the same as it was BEFORE I charged the system - which is ZERO on the gauge.
I really don't know how accurate the thing is. Should I spring for another can or look deeper into the system?
This leads me to think that either 1.) I did something really really wrong or 2.) There is a BIG ugly leak that suddenly sprang up overnight.
I should add that when I jumpered the wires at the pressure switch, the clutch "clicked" but the compressor did not switch on.