What's the proper procedure for adding R12 refrigerant?

This will help you Im sure its the same way as the 134 stuff.... to much will shut down compressor. Could be wrong however.

[ame="http://www.youtube.com/watch?v=ERDsfRRMuow"]YouTube - ‪Car Maintenance : How to Add Freon to a Car Air Conditioner‬‏[/ame]