An air conditioning system including a first compressor and a second compressor provided in parallel with the first compressor to vary compression capacity. The second compressor includes a housing having a compressing chamber, a vane that moves forward and backward in a radial direction of the compressing chamber, a vane guide groove formed in the housing to guide the forward and backward movements of the vane, and a vane controller that controls the operation of the vane in order to vary capacity. The vane controller includes a control valve that switches a fluid path so as to selectively apply suctioning pressure of the second compressor and discharge pressure of the first compressor to the vane guide groove and a controller that controls a fluid path switching operation of the control valve by a pulse width modulation (PWM) method in accordance with air conditioning load.