Vehicle air conditioner

A vehicle air conditioner includes a variable displacement compressor (10) forming a part of a coolant circuit, detectors (80-83) for detecting external information necessary for air conditioning, and a controller (79). The compressor (10) has pistons (35) and mechanism for actuating the pistons (35) to draw, compress and discharge refrigerant. The piston actuating mechanism is located in a crank chamber (15). The pressure in the crank chamber (15) is changed to vary the compressor displacement. The controller (79) controls the compressor (10) based on the information from the detectors (80-83). When disengaging an electromagnetic clutch (23), which is located between a vehicle engine (Eg) and the compressor (10), the controller (79) quickly decreases the compressor displacement and prevents the pressure difference between the crank chamber (15) and compression chambers (33a) excessively increased. Therefore, immediately after being stopped, the compressor (10) is started at the minimum displacement, which minimizes the shock due to load torque change on the engine (Eg). Also, the electromagnetic clutch (23) is prevented from malfunctioning.