A Thermo Fan stitch works similar to a thermistor except once it gets to a certain resistance it switches and allows current to flow through it.
I was asked to supend the thermo fan switch in a container of water and heat it up and read the temp with a thermometer and also read the voltage and plot it on a graph. The slope going down on the graph represents the thermo fan stwitch heating up because the resistance is going down and as soon as it gets to 45 degrees it stays at this very low resistance allowing voltage to push the current through.
However this thermo fan witch is fault because it switches on at a very low degree, it should switch on around 80-100 degrees depending on manufacturer.
As the coolant heats up it changes the resistance inside the thermo fan switch and when it gets to a certain resistance (low) it switches.
