Answer by
LeheckaG (1826)
Generally, "YOU" DON'T.
First, a U.S.-EPA (Section 608 stationary/universal, 609 motor vehicle) certified technician locates & plugs all refrigerant loop leaks;
Then the certified technician identifies the appropriate replacement refrigerant, conditioner-lubricant, and/or leak detection UV-dye; and recharges your system checking charge & operation with that refrigerant's hi/lo-side manifold gauge set.