Automotive Service Excellence (ASE) Air Conditioner Certification Practice Exam 2025 - Free ASE Air Conditioner Practice Questions and Study Guide

In automotive air conditioning systems, PAG (Polyalkylene Glycol) oil is commonly used in A/C compressors, particularly in systems designed for use with R-134a refrigerant. PAG oil has excellent lubricating properties, which are essential for the proper operation of the compressor. It is hygroscopic, meaning it can absorb moisture from the environment, which is beneficial in preventing ice formation within the system. This oil is specifically formulated to work with the chemical properties of R-134a and is favored due to its compatibility, thermal stability, and ability to reduce friction and wear in moving parts.

Mineral oil, while historically used in older A/C systems particularly with R-12 refrigerant, is not compatible with R-134a and can lead to compressor failures when used in modern systems. Esters oil is another type of lubricant that can be used, particularly in some application when retrofitting, but PAG is more commonly specified for most A/C systems today. Vegetable oil is not suitable for automotive A/C applications as it does not have the necessary properties to withstand the temperatures and pressures within the compressor and can break down quickly.

Thus, PAG oil is the preferred choice due to its superior performance characteristics in contemporary automotive A/C systems.