Vehicle air conditioning system with expansion valve control during high pressure cycle conditions

An air conditioning system, comprising:

• a blower for creating an air current;
• an air-conditioning duct that guides air produced by the blower into a compartment;
• a compressor having an intake port for taking in low-pressure refrigerant of a refrigerating cycle, a gas injection port for introducing intermediate pressure gas refrigerant of the refrigerating cycle, and a delivery port (22a) for delivering compressed high-pressure refrigerant;
• an inside heat exchanger mounted inside the air-conditioning duct for condensing high-pressure refrigerant from the delivery port of the compressor during heating;
• first pressure-reducing means for pressure-reducing high-pressure refrigerant from the inside heat exchanger to an intermediate pressure via an electrically-adjustable aperture;
• a gas-liquid separator for gas-liquid separating intermediate pressure refrigerant from the first pressure-reducing means;
• second pressure-reducing means for pressure-reducing intermediate pressure liquid refrigerant separated in the gas-liquid separator to a low pressure;
• an outside heat exchanger for evaporating low-pressure refrigerant from the second pressure-reducing means during heating;
• a gas injection passage for guiding intermediate pressure gas refrigerant separated in the gas-liquid separator to the gas injection port of the compressor;
• compressor speed controlling means for controlling an operating speed of the compressor;
• and
• controlling means for controlling the aperture of the first pressure-reducing means, for calculating, during heating, a pressure change rate based on information relating to high pressure of the refrigerating cycle, and for reducing the aperture of the first pressure-reducing means when the pressure change rate rises above a first predetermined value.