PURPOSE: To simplify the shipping work of automobile air-conditioner control units and to reduce the cost of the system thereof by automatically selecting and executing automatic air-conditioner control or automatic heater control according to whether or not a sensor is connected.

CONSTITUTION: Programs for controlling an automatic air conditioner and for controlling an automatic heater are stored in progress in a control unit 10. When a sensor 20 is not connected to sensor connection terminals H1, H2 a digitally-converted value FFH of a constant voltage (5V) is input to a microcomputer 11, while when the sensor 20 is connected to the terminals a value other than FFH is input so that the microcomputer 11 determines whether or not the sensor 20 is connected. When the microcomputer 11 determines that the sensor 20 is connected, the mode of automatic air conditioner control is selected and executed. When the microcomputer determines that the sensor 20 is not connected the mode of automatic heater control is selected and executed.