If all else fails, read the instructions :idea::laugh:. According to Vintage Air, it takes just over two cans (28.8 oz) to fill the system. I've got a little less than two cans in right now.
http://www.vintageair.com/Instructions2013/900004.pdf
Tools used to fill the system:
Harbor Freight vacuum pump: Vacuum Pump - AC Vacuum Pump w/ R134A & R12 Connectors
Manifold Gauge Set: AC Gauges - Save on this AC Manifold Gauge Set
Pete, When we vacuumed the system, we let it sit overnight to check for leaks. Don't know if you did that, but it's not a bad idea.