bellows 64 can be varied freely by changing the spring constant thereof in a refrigerating system for a vehicle air conditioning circuit including a compressor of above mentioned construction when the load is increased to heighten the suction pressure of the compressor the bellows 64 is in contraction below the fixed stopper 61 allowing the suction valve 17 to be regulated by the fixed stopper 61 in the similar way to the conventional art when the load is reduced in the running to throttle the expansion valve followed by the descending of the suction pressure of the compressor the bellows 64 is expanded to elevate the top surface thereof higher than the tip of the fixed stopper 61 the lift amount of the suction valve 17 is regulated smaller by the movable stopper 62 than by the fixed stopper 61 this brings about a reduction of suction efficiency of the compressor and consequently reduces the working amount of the compressing process followed by the reduction of required motive force for preventing an excessive falling of the inside temperature of the evaporator in a fifth embodiment shown in fig9 a movable stopper 70 is mounted in a recessed portion 71 at a confronted position with the tip of the suction valve 17 being adjustable of its position by a bellows 73 disposed in a vacant space 72 formed in the cylinder block 1 movable stopper 71 is attached to the tip of a rod 75 placed on a bottom plate 74 of the bellows 73 which rod 75.