PURPOSE: To prevent generation of upblow sound caused by excessive engine output in a titled controller equipped with engine drive variable capacity compressor of an air conditioner for vehicles by determining the capacity of a compressor based on the heat load in the car room, and controlling the idling speed of an engine based on the result.

CONSTITUTION: The detected signals of a room temperature sensor 14, outside air temperature sensor 15, and duct sensor 16 are input in the interpretation control section 11 of an air conditioner control unit 10 becoming the signal of an engine control unit 40 to control a compressor control section 12 and air condition unit 9. At the same time, the heat load in the car room are sent from the interpretation control section 11 to a compressor capacity determination section 38 to determine the capacity of a variable capacity compressor 2 corresponding with a heat load and controls the idling speed of an engine E through an idling speed control section 39. This constitution can prevent the generation of upblow sound caused by excessive engine output.