Air conditioning system for automotive vehicles

In an air conditioning system for an automotive vehicle having a passenger compartment, including a compressor having a driving shaft driven by an automotive engine having an output shaft to compress refrigerant circulating in said system, an electromagnetic clutch interposed between said driving shaft of said compressor and said output shaft of said engine, a condenser for cooling the refrigerant compressed by said compressor to liquefy same, an expansion valve for controlling the flow rate of the liquefied refrigerant to proper values corresponding to thermal load on said air conditioning system, an evaporator for evaporating the liquefied refrigerant to cool air to be blown into said passenger compartment through heat exchange thereof with the refrigerant, a temperature sensor and a pressure sensor for detecting, respectively, the temperature and pressure of the refrigerant at an outlet of said evaporator, and an expansion valve control means for controlling the opening of said expansion valve in response to output signals from said temperature sensor and said pressure sensor,

• the improvement comprising:
• electronic control means in which said expansion valve control means is provided, said electronic control means including conversion means for electrically converting the pressure of refrigerant detected by said pressure sensor to a corresponding saturation temperature of the refrigerant, and determining means for electronically determining whether or not the quantity of the refrigerant in said air conditioning system is smaller than a required valve through comparison of the difference between the temperature of the refrigerant detected by said temperature sensor and the corresponding saturation temperature of the refrigerant obtained by the conversion by said conversion means with a predetermined reference value, said determining means including means for determining whether or not the quantity of the refrigerant is smaller than said required quantity immediately after the start of said compressor;
• and
• indicator means controlled by said electronic control means for indicating the existence of an abnormality when said determining means determines that the quantity of the refrigerant is smaller than said required value;
• said expansion valve control means also being operable to interrupt power transmission from said engine to said compressor by disengaging the electromagnetic clutch when said determining means determines that the quantity of the refrigerant is smaller than said required value.