You need to evacuate the system, replace the o ring, use a vacuum pump to remove any air and moisture afterwards and then recharge the system.
In other words take it to a shop that has the proper equipment to do the above.
96 T/A, Black/Graphite Leather, T-Tops, 6 speed, 10 speaker Delco/Bose "Monsoon"
Original owner, 187k miles and counting.
Total engine rebuild at 187 K miles.
Complete AIR delete
Bored .030 over.
Comp cams Xtreme Energy LT1 266HR-14 street cam.
lift I .500 E .510 duration I 266 E 276