I should add this. The reason the manufacturer wants to have you use the can upright is that it is possible to dump too much liquid into the system and damage the compressor. So, do it slowly. In the AC industry we always charge with the can upside down, or large bottle. Even with R12, if you fully charge a system from scratch it will make the refrigerant too cold to boil off. So the trick is to use the can upside down, but charge slowly since a little liquid makes a lot of vapor once inside the system.