First of all, the system should have been charged based on operating pressures rather than by volume since the values for R12 vs R134 are not to be treated as the same. Charging it this way would also have indicated any other problems you may have have (like a bad expansion valve). Lack of airflow across the condenser can also be caused by a build up of dirt and leaves on the front side of the radiator. Have you checked that? If not clean it with a pressure washer or at least a garden hose.
