PAG Oil
Polyalkylene Glycol lubricant, a synthetic oil used in automotive air conditioning systems to lubricate the compressor.
PAG (Polyalkylene Glycol) oil is a high-performance synthetic lubricant used specifically in automotive air conditioning systems. Its primary role is to lubricate the moving parts of the A/C compressor, preventing wear and overheating. PAG oil is highly soluble in modern refrigerants like R-134a and R-1234yf, allowing it to carry through the A/C loop and return to the compressor during operation.
PAG oil is extremely hygroscopic, meaning it rapidly absorbs moisture from the surrounding air. If an A/C system is left open to the atmosphere during a repair, the PAG oil will absorb water, forming acids that corrode the aluminum evaporator and condenser tubes and damage the compressor. PAG oil is available in different viscosities (such as PAG 46, PAG 100, and PAG 150), and using the wrong viscosity can lead to compressor failure.
Symptoms of oil starvation or incorrect PAG oil usage in an A/C system include a noisy compressor clutch, compressor lockup, and poor A/C performance. When replacing A/C components like the compressor, condenser, or evaporator, technicians must measure and add the correct amount of PAG oil to maintain the system's total oil balance. Any system open for repair should have its receiver-drier replaced to remove moisture.