If you did not at least replace the two schrader valves be prepared to loose all that R12 in pretty short order. Amongst other concerns, this weak point in R12 systems was one of the major upgrades when they went to quick-disconnect fittings for R134A. I am not sure if it was the automitive environment, quality of the parts or other factors but one or both of the valves invariably leak if the system has been depressurized for any period of time.

And HVAC proefessionwill have a handy little tool for replacing the while still leaving almost all of the freon in the system and I am sure they are available to the rest of us but I have just never looked for one.