In this study, a quantitative analysis regarding the effect of A/C on the fuel consumption was conducted. The contribution of each individual component of the A/C system to the fuel consumption was studied at five different vehicle speeds. The results are summarized: (1) A new approach to analyse the influence of each component on the fuel consumption was developed through a systematic sequence of processes. The driving torque of the alternator was obtained through a single-component experiment. The effect of the electric load applied to the alternator on the driving torque was then measured. Linear recursive equations from these data were used to derive the driving torques of the blower, the cooling fan and the clutch. The driving torque of the compressor was verified by installing a refrigerant line and a blower on the compressor. Finally, the contribution of each A/C system component to the fuel consumption was calculated. (2) The fuel consumption increased linearly with increasing engine load at a constant speed. A linear recursive equation of the fuel consumption versus the engine torque was derived from the experimental data. The estimated fuel consumption and the measured data showed an error of less than 3.2%. (3) As the vehicle speed increased, the absolute value of the fuel consumption increased with the A/C on; however, the rate of increase decreased in comparison with the operation without A/C. The driving torques of the compressor and of the alternator also decreased as the vehicle speed increased. However, the portion of the driving torque of the compressor increased, whereas that of the alternator became relatively small. The contributions of the other components (the blower, the cooling fan and the clutch) to the fuel consumption had constant values regardless of the vehicle speed. (4) Among the A/C system components, the most important component affecting the fuel consumption is the compressor which caused a fuel consumption increase of 77-89%. The contributions in order after this component are as follows: from the blower, 6-12%; from the cooling fan, 4-10%; from the clutch, 0.7-2%.