Control circuit for a refrigerating system

Control circuit for a refrigerating system of the type comprising:

• an electric motor of a hermetic compressor having a main winding and a secondary starting winding;
• a first temperature sensor to be disposed inside a refrigerating cabinet to constantly detect the inner temperature of the cabinet;
• a second temperature sensor disposed adjacent to the compressor shell to constantly detect the temperature of the compressor shell;
• a current sensor in series with the electric circuit that feeds the compressor to detect the current drawn by the motor;
• a first operable electronic driving switch, which selectively communicates a power source with the main winding of the motor, when in a closed operative condition of the compressor operation, and interrupting said communication when in an open operative condition;
• a second operable electronic driving switch, which selectively communicates the power source with the starting winding of the motor, when in a closed operative condition of the compressor start, and interrupting said communication when in an open operative condition, which is automatically obtained after a determined time interval for the closing of the second operable electronic driving switch;
• a central processing unit, supplied by the power source and operatively connected to said first and second driving switches to command the operation of said first and second driving switches as a function of the temperature and current operative conditions detected by the sensors, said central processing unit instructing the closing of both the first and second driving switches when the temperature inside the refrigerating cabinet, detected by the first temperature sensor, reaches a maximum value of a predetermined temperature range, and opening the first driving switch when the detected temperature equals the minimum value of said temperature range;
• said central processing unit instructing the closing of both the first and second driving switches when the average temperature of the compressor shell detected by the second temperature sensor is lower than the maximum predetermined operative value, and causing the opening of the first driving switch when the average temperature surpasses said maximum value, even if the temperature inside the cabinet is higher than the maximum desired value, said central processing unit instructing the opening of at least the first one of the driving switches when the magnitude of the average current drawn by the motor, said current being the one drawn by the motor and detected by the current sensor and integrated in a determined time interval by said central processing unit, surpasses a maximum predetermined operative value even if the temperature of the motor is within its acceptable operative range and the temperature inside the cabinet is higher than the minimum desired value.