1973 Dodge Charger How do I recharge the R-12 Freon 1973 Do

Air Conditioning problem
1973 Dodge Charger V8 Two Wheel Drive Automatic

I have the Freon and the home refill hose.
I have never charged the system after changing the engine in 1992. The components are all there, I replaced the seals, the o rings and cleaned out the drier and had the condensor coils dippped and rebuilt professionlly. How do I get by the low pressure switch and how do I know which port is the low pressure port?