Vehicle air conditioner with variable displacement compressor

In a vehicle air conditioner, a variable displacement compressor has a control valve for continuously changing a discharge capacity of the compressor, and a control unit calculates an electrical value DT to be applied to the control valve based on the following formula of DT=DT(n−1)+Kp[(En−En−1)+C/(Ti×En)]. In this formula, En=Te−Teo, Kp=Kp′/(Ph×Ph′), Ti=Ti′/(Ph×Ph″), C is a sampling cycle, n is a positive number, Kp′, Ti′, Ph′and Ph″ are constants, Ph is a refrigerant pressure at a high pressure side, Te is a detected air temperature at an air outlet of the evaporator, and Teo is a target evaporator air temperature that is calculated based on an outside air temperature Tam. Accordingly, the compressor can be stably controlled in a wide thermal load range.