"1 LB. 14 OZ. of R 12" according to a sticker I saw on a '73 with factory AC. That number might be different with R134, and will almost certainly be different if you have swapped out the compressor, hoses, condenser or anything else with parts that are a different size than stock. My AC is a factory setup except for bigger hoses, drier and a different, cross-flow condenser. Ended up using just over two cans of ES-12a, which is yet another refrigerant that will end up being a different amount than either R12 or R134. I'd say unless you have a totally stock system and a supply of R12, charge by pressure instead of volume.
