Air-conditioning system for vehicle and its control method

An air-conditioning system for a vehicle, including a refrigerant circuit and an engine, comprising:

• a battery for supplying electric power;
• a compressor operative to compress refrigerant gas for the air-conditioning system;
• an electric motor electrically connected to the battery, the motor being driven due to the electric power, and operatively coupled to drive the compressor when the motor is energized;
• and
• a load torque control mechanism responsive to the operating condition of the engine to control the load torque of the compressor below a predetermined value during times when the motor is driving the compressor;
• wherein the compressor is a variable type compressor having a control chamber, the displacement of the compressor is varied in accordance with variation of pressure in the control chamber, the pressure in the control chamber is varied by adjusting the opening size of a control valve, the control valve comprising:
• a pressure sensing mechanism for mechanically detecting pressure difference between first and second pressure monitoring points located in the refrigerant circuit;
• a valve body moved by the pressure sensing mechanism such that the displacement of the compressor is adjusted so as to counter the change in the detecting pressure difference based on a set pressure difference;
• means for varying the set pressure difference disposed in the control valve by adjusting force acting on the valve body due to an external command;
• and
• wherein the control valve varies the set pressure difference.