R-134a A/C refrigerant guide of Subaru cars:

Expansion Valves

The expansion valve set points for an R-134a system are different from the setting of an R-12 expansion valve, to compensate for the slight difference in operating pressures and efficiency ratios. Subaru expansion valves are not field serviceable, and should always be replaced if faulty. Again, proper identification when replacing system components will be critical on future A/C systems.

Refrigerant Hoses

Refrigerant hoses on many of today’s R-12 systems are constructed with barrier type inner linings. This helps minimize the permeation of refrigerant over long periods of time. These types of hoses will also be used on R-134a systems.

Another important note to remember about hoses, and other pipe assemblies, is that manufacturers have intentionally changed mating connections in many cases, to help prevent accidental inter-mixing. Be specific when ordering replacement components to avoid costly delays.