A/C Blows Warm Air

My a/c was blowing warm air. I saw that the compressor clutch wasn't engaging. When I jumped the low pressure switch, the clutch came on, so I rented a pressure gauge manifold from autozone and attempted to add some refrigerant. After starting the car, turning the a/c on, turning the fresh air blower on, and jumping the low pressure switch, I started adding the refrigerant. I added maybe a half a can before noticing the high pressure was at zero (low pressure at about 35 after adding some refrigerant). Anyways, does this mean my compressor is toast, or could it be something else?

I'm no expert by any means, so take this with a grain of salt.
If you had no gas in the system, you've got a leak. Why not put a can in, slowly, and look / listen for leaks? (with the engine off). You might try a can with die in it to help locate the leak. If the pressure stays up for a couple of days, I figure you don't have a leak, and it could be a compressor problem.
I had a stupid fault in that the the plastic cap over the valve was pushing the valve open, letting the gas out. Good luck