Method of controlling an air conditioner for vehicles

A method of controlling air conditioner for vehicles wherein the target control value of the pressure control valve which controls tilt angle of a swash-plate of a swash-plate type variable capacity compressor is variably controlled according to the temperature deviation between target evaporator temperature and actual evaporator temperature, thereby efficiently controlling the discharge capacity of the compressor. The method of controlling air conditioner for vehicles of the present invention comprises the steps of: calculating target heat discharge quantity (S110); determining on the high thermal load control or low thermal load control from the calculated target heat discharge quantity (S130); and compulsively controlling the control value (Duty) of the pressure control valve of swash-plate type variable capacity compressor according to the amount of the thermal load firstly (S140), and then normally controlling the control value secondly (S180). By compulsively controlling the control value of the compressor according to the amount of the thermal load decided from the target heat discharge quantity firstly, and then normally controlling the control value secondly, the actual evaporator temperature can reach the target evaporator temperature at initial stage of the operation and temperature stability can be secured.