This circuit will operate a low voltage cooling fan when the temperature rises above a set point.
The sensor should not be placed directly in the path of the fan.
The temperature at which the fan will operate can be controlled by VR1 on the Comparator Switch.
Circuit Voltage: 6 to 12 volts - should be chosen to match the voltage of the fan.
Adjust VR1 with a screwdriver to the center position.
If the temperature you require is outside the range of VR1 on the Comparator Switch, then adjust VR1 on the Heat Sensor
The Schmitt setting should be selected by moving the jumper to the right, creating hysterisis in the switching.