Compressor Oil

The compressor oil used in the R-134a system is drastically different than the mineral oil based lubricant used in R-12 systems. R-134a systems require Polyalkylene Gycol lubricants, often referred to as "PAG" oil. The proper PAG oil for use in BMW R-134a systems will be made available through normal parts channels. Use of R-12 compressor oil in R-134a systems will cause the compressor to seize and fail. The R-12 mineral oil does not stay in solution in R-12a. In addition, R-134a compressor PAG oil should not be used in an R-12 system. Long term damage and corrosion will result. The green R-134a system labels, usually located near the top side of the fan shroud in the engine compartment, will display the refrigerant/PAG oil requirement for R-134a systems. R-12 systems will have a BLACK sticker located in a similiar place. Examples are illustrated.


PAG oil should only be stored in its original container, and sealed as tightly as possible. PAG oil is totally devoid of moisture when packaged, and will absorb moisture readily (hygroscopic) if exposed to the atmosphere, rendering it useless. Dispose of all extracted lubricants from A/C systems. Never reuse old compressor oil. Contaminated PAG oil should never be added to the air-conditioning system, and old PAG oil is typically contaminated with moisture. R-134a is even more sensitive to moisture contamination than R-12 systems, and because of the desiccant material change (refer to "Receiver-Dryer"), the capacity per volume of the receiver-dryer is typically less.