PURPOSE: To improve car fuel cost by making a suction control valve, positioned in the refrigerant inlet, freely operable through a negative pressure actuator connected to the negative pressure source, in an engine driven refrigerant compressor.

CONSTITUTION: When the number of revolution, i.e., the engine load, is small, the negative pressure in the intake manifold is large, and bellows 21 is constricted against a spring 22, widely opening the inlet 11 of refrigerant compressors 8 and 9, to carry out smooth circulation of refrigerant. As the engine load increases, the negative pressure approaches the atmospheric pressure and a suction control valve 20 starts to close the inlet 11, restricting the circulating quantity of refrigerant and, therefore, suppressing the increase in the load of the refrigerant compressor, i.e., the engine load. Thus, the work for unnecessary circulation of refrigerant is excluded, improving the car fuel cost, while the acceleration capacity is not failed when the cooler is in used. And, being continuous controlling, the riding comfortableness is not affected.