Hello,
A thermistor is a type of resistor whose resistance varies significantly with
temperature. The one described here has a negative temperature coefficient
meaning that the resistance decreases as the temperature increases. It is wired in
series with the fan and switch across the
battery. So, as the temperature
of the
refrigerator compartment increases, the resistance of the thermistor
decreases and the fan speeds up. I put a similar setup on my rig but left out
the thermistor... I just let the fan run all day when the weather is hot. The
thermistor in the circuit will save a little bit of juice.
Larry H