This electronic car thermostat circuit described here regulates the air blower system of a car. When the temperature inside the car exceeds a certain preset level T1 tuns on the fan. A temperature dependent resistor NTC (thermistor) is used as a sensor. The resistance of this resistor must be 47kΩ at 25oC.
The car thermostat circuit is calibrated through potentiometers P1 and P2 so the air blower will turn on one the threshold temperature is reached. P2 sets the “ON” level and P1 the “OFF” level.
To calibrate the car thermostat circuit: first set P1 at middle position and slowly adjust P2 untl the fan turns on. The temperature value must be the desired threshold level at this moment. Later when the temperature has gone down, adjust P1 until the fan stops.
Sent by Mihai George, Romania. Thanks.