In this paper, the key ejector geometry parameters for an air-cooled ejector cycle using R134a with cooling capacity of 2 kW are designed by 10 analysis. Through enlarging the designed area ratios by connecting the replaceable nozzles with a main body, optimum area ratios under air-conditioning working conditions are studied experimentally. Three parameters, namely, the entrainment ratio, COP and cooling capacity are evaluated, and the results show that the optimum area ratios are from 3.69 to 4.76 that are lower than those mentioned in other studies. With a fixed area ratio, experiments also show that the influence of the ejector area ratio on the ejector performance largely depends on the operating conditions. Consequently, the effects of operating conditions such as primary flow pressures on the ejector system performance are evaluated. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.