R-134a A/C refrigerant guide of Subaru cars:
The service valve on an R-134a container has a thread size that is different from an R-12 container. The service gauges and fittings are different, and should never be adapted to interchange between R-12 and R-134a systems.
The construction and appearance of most R-12 and R-134a components is usually very similar. However there are several critical and significant changes between the two systems. For instance:
• Compressor lubrication for R-134a systems requires a new type of refrigerant oil.
• Condensers for R-134a systems require greater efficiency, since high side operating pressures tend to be slightly higher than those of an equivalent R-12 system.
• R-134a type receiver driers contain a different type of desiccant.
• Expansion valve set points are different.
• Refrigerant hoses are constructed of less permeable material.
Intermixing of components, refrigerants, or lubricants is not recommended due to the risk of hindering performance, and possible system failure. That’s why manufacturers of automotive A/C systems and components are placing extra emphasis on labeling and identification.