Hi Bruce. When retrofitting GM vehicles early on, that did not have a published specification, this formula from GM worked fine. (R12 spec charge X 0.9) - 0.25 lb = R134a charge.

E.g. 3.42 lbs X 0.9 = 3.078 - 0.25 lb = 2.83 lbs R134a, which is approximately ... Login to read more.