Vehicle air conditioner and method for controlling vehicle air conditioner

A vehicle air conditioner including a refrigerant circuit that incorporates a variable displacement compressor (40) driven by an engine (E) of the vehicle. The air conditioner includes a control valve (CV) for varying the displacement of the compressor and an ECU (72) for controlling the control valve. The control valve has a bellows (48; 90), a valve body (46), and a coil (61). The ECU varies the displacement of the compressor by energizing the coil to apply a force, which counters the movement of the bellows, to the valve body to move the valve body. This alters the moved amount of the bellows. The air conditioner control unit gradually changes the force applied to the valve body by the coil to adjust the pressure difference and vary the displacement of the compressor when the engine is running at an idle speed.