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The thermistor is a temperature-sensitive resistor that usually has a negative temperature coefficient. This means that an ohmmeter can be used to test the thermistor if it's isolated or removed from its circuit and power source. As heat is added to the thermistor, its resistance should drop. One needs to have some data about the thermistor's temperature curve to know at what temperature the resistance becomes 0 Ω. If the temperature is in the middle of the thermistor's operating range, the amount of resistance change should be much larger than an RTD. For example, the resistance of one standard type of thermistor material would have 19.59 k Ω at 0°C and 407 Ω at 100 °C.
If the resistance of the thermistor does not change, or if the value is always infinity ∞, the thermistor is defective and must be changed. The infinity reading indicates the thermistor has an open, but one must use a very high resistance scale on the meter and try to increase the temperature as much as possible to get the resistance to move lower.
