A steady-state mathematical model of the automotive air conditioning system with a variable-displacement compressor (VDC) is developed to find out the reasons causing evaporator frosting. To validate the system model, a test system is established and the simulated results are compared with experimental data: the predicted results agree well with the experimental data. After analyzing the influence of different factors with the system model, three reasons causing evaporator frosting have been found and corresponding countermeasures have been proposed: (1) the system performance band caused by the frictional forces among the moving components of the VDC can contribute to evaporator frosting, which may be avoided by decreasing the frictional forces between the moving components while designing, manufacturing and operating the VDC; (2) the mismatch between the parameters of the control valve and the resistance pressure of suction pipe or the condenser size can also contribute to evaporator frosting and the control valve with a proper initial compressive force should be selected for a given suction pipe and condenser; and (3) a higher air temperature at the condenser's inlet may cause evaporator frosting one needs to consider the influence of the air temperature at the condenser inlet while designing the new control valve. (c) 2004 Elsevier Ltd. All rights reserved.