What was a key design change for hfc-134a a/c systems versus cfc-12 a/c systems?

Answer : According to Society of Automotive Engineering (SAE) standards the major key design change that was done for CF-12 A/C systems to HFC-134a A/C systems for the mobile A/C system service is that it provided with new service fittings which reduced the venting of refrigerants into the atmosphere and hence the mixing was also reduced with the ozone.

This new, unique and advanced quick modification has helped a lot in terms of maintaining low level of CFC emission in the environment.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).