Controller and method for controlling compressor of vehicle air conditioner

A controller (70) for improving the durability of a compressor employed in a vehicle air conditioner without decreasing engine fuel efficiency. The controller detects the driving conditions of the vehicle and determines whether the engine (E) is in a reversely driven state, in which vehicle wheels (W) drive the engine instead of the engine driving the wheels. The controller increases the amount of refrigerant discharged from the compressor when the engine is in the reversely driven state.