Jin, S. and Hrnjak, P., "Refrigerant and Lubricant Distribution in MAC System," SAE Int. J. Passeng. Cars - Mech. Syst. 6(2):1013-1020, 2013, doi:10.4271/2013-01-1496.
This paper presents experimental results for refrigerant and lubricant mass distribution in a typical automotive A/C (MAC) system.Experiments were conducted by closing valves located at the inlet and outlet of each component after reaching steady state, isolating the refrigerant and lubricant in each component. Refrigerant mass is recovered in a separate vessel using liquid nitrogen to reduce refrigerant vapor pressure to near vacuum. The overall weight is determined within ±1% after the separation of refrigerant and lubricant. The mass of lubricant is determined by using three different techniques: Remove and Weigh, Mix and Sample, and Flushing. The total mass of lubricant in the system is determined with ±2.5% uncertainty on average. R134a and R1234yf are used with PAG 46 oil as working fluid at different Oil Circulation Ratio (OCR), ranging from 2% to 4%. Experiments are conducted in two standard testing conditions: I35 and L35 (SAE Standard J2765).R134a and R1234yf exhibit similar results in terms of refrigerant and lubricant retention. Higher mass flow rate does not significantly change the refrigerant distribution, but a lower lubricant retention in the evaporator is observed. It is found that only about a quarter of the total mass of lubricant resides in the compressor.