My Gen 1 had been setting for 6 yrs. Still had a little R-12 in it.. So I removed it ( the approved way).Pulled a vacuum on it for 2 hrs.Let it set for 1 hr w/ no change in vacuum. Then put in the 134-a.Picked up the 3 can kit w/ charging hose from Advance auto. The instructions stated to put in 80% of the original R-12 charge. It's been working fine for 2 &1/2 yrs...Just for what it's worth. Good luck.

Va_Stumpy
89 Raider
"Never judge horsepower by exhaust"
3.0
automatic
stock as a rock
Dual Bouncy Seats