Temperature control circuit for automobile air-conditioning system

Abstract

A temperature control circuit of an automobile air-conditioning system includes a temperature sensor for detecting the temperature of air blown into the room of the automobile. The signal detected by the sensor is compared at a first comparator with a voltage level corresponding to a predetermined temperature. The output of the first comparator at a time when the blown air temperature is lowered to the predetermined temperature, is delayed by a delay circuit and is applied to a second comparator. Then, the second comparator generates a signal for stopping the operation of the refrigerant compressor. The signal is also applied to a third comparator which maintain the stop signal until the signal corresponding to a higher temperature is applied thereto from the temperature sensor. Thus, the frost on the refrigerant evaporator can be defrosted before the compressor restarts. A fourth comparator is used for controlling the temperature of the room of the automobile. Temperature detected signal from the temperature sensor or another sensor disposed in the room is compared with a variable reference signal at the fourth comparator, from which a similar signal for stopping the operation of the compressor at a time when the detected temperature is lowered to a temperature corresponding to the variable reference signal.