Which lubricant is most commonly used with R-134a refrigerant?

The most commonly used lubricant with R-134a refrigerant is PAG (Polyalkylene Glycol) oil. This type of oil is specifically formulated for use with refrigerants that require a synthetic lubricant. R-134a, being a hydrofluorocarbon (HFC), is chemically incompatible with mineral oils which do not mix well with it. PAG oils provide excellent lubrication properties and also have good thermal stability, which are crucial for the proper operation of refrigeration systems using R-134a.

In contrast, mineral oil is derived from crude oil and is typically used with older refrigerants like R-12. Alkyl-benzene oils may be used in some applications but are not as widely preferred for R-134a as PAG oils. Polyester oils, while they can also be compatible with some refrigerants, are less common specifically for R-134a compared to PAG oils, which has become the standard due to their superior performance characteristics. Thus, PAG oils' compatibility and efficiency make them the go-to choice for systems utilizing R-134a refrigerant.