Refrigerant and Oil

Under no circumstances may an A/C system using R134a be filled with the earlier R12 refrigerant. Furthermore, only PAG (PolyAlkylene Glycol) oil may be used with R134a. Two different PAG oils are available depending on the make of compressor installed in the car. When filling with oil, it is extremely important that the correct grade for the particular compressor is used. The PAG oils may not be interchanged or mixed. The correct PAG oils for the various compressors using refrigerant R134a are shown in the table below.

The following will occur if refrigerant R12 is used in a system designed for R134a:
- The compressor will overheat and seize.
- The working temperature will become excessive, leading to failure of hoses and seals.

Similarly, a system designed for R12 will suffer damage if filled with R134a or with PAG oil.