What was the key design change for hfc-134a a/c systems versus CFC 12 a/c systems

Reduction in the contribution to ozone depletion and reduced Global Warming Potential - Both gases CFC and HFC gases are used as refrigerants in car air conditioning systems (A/C-systems). However, hfc-134a a/c systems were built to be environment friendly and reduced the Global Warming Potential (GWP) by more than 80%.