There is a chart somewhere, I think it can be found in Alldata. I'll try and dig it out.
X number of ounces of PAG oil will remain in a properly evacuated system. X ounces in the compressor, X in the condenser etc etc.
With your Bonneville, you would need to drain the cooling system and remove the radiator, then the condenser. Those fittings need big wrenches and make sure you use an opposing wrench. Meaning, 2 wrenches on each fitting to prevent twisting the aluminum line.
Once all replaced, your going to need to evac the system and put a vacuum on it again. Then charge with X ounces of PAG oil you lost, then its 2.2 lbs of R134a. And yes, YOU do need to put a vacuum on the system so you get a proper re-charge of freon and remove any moisture that got in.
1997 Pontiac Bonneville SEi-SCRAPYARD
2000 Chevrolet Blazer LT 4X4 4.3L
2002 Chevrolet *-10 LS Ext Cab 4X4 5.7 V8