The term thermistor refers to a "thermal resistor". It is basically a resistor that changes due to the surrounding temperatures. There are two types of thermistor. NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient) types. NTC type thermistors will gain resistance as the temperature drops, as PTC types will gain resistance as the temperature rises.
The thermistor i was to test was an NTC type, which means the resistance should start to drop once i apply heat to it. I hooked it up to a power supply and a multimeter, and placed it in a container of water. I then applied heat in the form of a stove element, and used a thermometer to track temperature as i recorded my results.
Water temp Resistance
33°c 1.36K ohm
35°c 1.33K ohm
40°c 1.14K ohm
45°c 0.96K ohm
50°c 780 ohm
55°c 680 ohm
70°c 407 ohm
75°c 390 ohm
The results above show a steady decrease in resistance as the temperature rises. It is within specification and is good for continued use.
Thermo Fan Switch
A thermo fan switch is very similiar to a thermistor, in that it is affected by temperature, yet instead of gradually changing with the temperature, it is set to switch at a pre-determined temp.
In testing the switch, we must measure the resistance across it, and determine the temperature it will switch at while applying heat to it.
Temperature Resistance
Room Temp 70.5 ohm
45°c 0.8 ohm
50°c 0.7ohm
55°c 0.9ohm
This particular thermo switch is far beyond spec, as it is switching at only 45°c. The specification for this fan is 80°c. So it is unserviceable and must be replaced.
you needed to take your fan switch up to at lest 90 degrees to make it operate
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