Abstract: The air-conditioning (AC) system of a modern passenger car is a thermodynamically demanding subsystem that consumes 5–20 % of the vehicle's total energy under typical operating conditions. The choice of refrigerant directly determines the system's cooling performance, energy efficiency, and environmental impact. This paper examines the engineering implications of replacing R-134a, the dominant car AC refrigerant from the early 1990s through the mid-2010s, with R-1234yf, the hydrofluoroolefin (HFO) now mandated by international regulations on low global-warming-potential (GWP) refrigerants. The paper describes the architecture and operation of a typical car AC system, formulates the governing thermodynamic equations of the vapor-compression cycle, and synthesizes peer-reviewed experimental data. Drop-in substitution of R-1234yf for R-134a in unmodified car AC hardware reduces cooling capacity by 4–9 %, lowers the coefficient of performance (COP) by 3–7 %, increases refrigerant mass-flow rate by 10–14 %, and lowers compressor discharge temperature by 7–12 K, with the penalty growing at high ambient temperatures. Component-level optimization—particularly the addition of an internal heat exchanger and increased subcooling—can recover most of the lost performance. The paper concludes with a discussion of trifluoroacetic acid (TFA) atmospheric breakdown, proposed PFAS restrictions, and the role of integrated heat-pump systems in electric vehicles.
Keywords: car air conditioning, automotive HVAC, R-1234yf, R-134a, HFO refrigerant, vapor-compression cycle, coefficient of performance, electric-vehicle thermal management.
Title: Refrigerant Performance in Passenger-Car Air-Conditioning Systems: A Comparative Analysis of R-1234yf and R-134a
Author: Mr. Said Abdelaal Saleh Khattab, Eng. Ali Mejbel Aljadei
International Journal of Mechanical and Industrial Technology
ISSN 2348-7593 (Online)
Vol. 14, Issue 1, April 2026 - September 2026
Page No: 29-37
Research Publish Journals
Website: www.researchpublish.com
Published Date: 07-May-2026
