R-12 refrigerant capacity for '84 W126 is 2.9 lbs (46.4 oz.)


But before you go any further - did you...

1.) locate and correct all leaks?

2) thoroughly flush all mineral oil out of the system and replace it with a R-134a compatible lubricant? Note oil replacement includes removing the compressor and draining/measuring the oil removed. Which lubricant did you use - PAG or ester? And how much did you add?

3) renew the receiver/drier?

4) pull a vacuum of sufficient duration and depth? A reading of zero is unsuitable.