Basic System Differences: R-12 vs R-134a
- R-134a pressures are higher than R-12, as temperature increases.
- Compressor oils:
- R-12 systems use mineral oil.
- 134a Systems use PAG oil.
- Underhood labels:
- R-12: black.
- R-134a: green.
All R-134a systems use quick-release service fittings.
Green R-134a Underhood Label:
LUBRICANTS
The compressor oil used in an R-134a system is very different from the mineral oil-based lubricant used in R-12 systems. R-134a systems require PAG oil. R-12 systems use mineral oil.
PAG oil should not be used in an R-12 system. Mineral oil should not be used in an R-134a system.
PAG oil should be stored in its original container and sealed as tightly as possible. It is very hygroscopic. (it absorbs water readily). When exposed to the atmosphere it rapidly absorbs moisture and should be discarded.
The green R-134a system labels, usually located near the top side of the fan shroud in the engine compartment, display the refrigerant/PAG oil requirement for R-134a systems.
Technicians should not reuse old compressor oil, since it is likely to be contaminated with moisture. An R-134a system is even more sensitive to moisture contamination than an R-12 system.
EXPANSION VALVES
The R- 134a system expansion valve uses a different operating pressure range. This enables the valve to work more efficiently with the new refrigerant. An expansion valve designed for use in an R-12 system, if installed in an R-134a system, may not allow enough refrigerant into the evaporator. This may affect the performance.
RECEIVER/DRYERS
R-134a Receiver/Dryer:
The basic design of R-12 and R-134a receiver/dryers is the same. However, while R-12 systems typically use silica gel as a desiccant, R-134a systems use zeolite. The drying capacity (per weight) of zeolite is only about 25% that of silica gel so R-134a receiver/dryers are larger; to accommodate larger amounts of desiccant. In addition, the high-pressure cutoff switch is rated higher for an R-134a receiver/dryer, since the system operates at higher pressures.