An air-conditioning system control apparatus for controlling an air-conditioning system of a vehicle equipped with a motive power engine, having: a device for determining whether there is a history of a load that has been applied to a compressor, operated by the output of the motive power engine, equal to or greater than a threshold, during operation of the air-conditioning system; a device for carrying out initial operation process of the air-conditioning system if the load history determination device determines that there is a history of a load equal to or greater than the threshold has been applied to the compressor; and a device for carrying out liquid accumulation resolution process when liquefaction of a refrigerant occurs in the compressor only if the load history determination device determines that there is no history of a load equal to or greater than the threshold has been applied to the compressor.