Heater Core Temperature Sensor / Switch: Description and Operation

- Coolant temperature sensor is resistor of the NTC (negative temperature coefficient) type, the resistance of which falls with rising temperature. The resistance is 9.9K Ohms at 25 °C (77 °F).

- Mounted at the heater actually measures the air temperature immediately adjacent to the unit. This prevents the blower from starting at the highest speed in the automatic mode before the coolant has begun to heat up. The blower speed increases gradually with coolant temperature.

- The system FUNCTIONS even if a sensor is faulty. To prevent the entire unit from being disabled if a sensor becomes faulty, the system is programmed to continue operating in a more or less normal manner in this event. However, it will react more slowly and will control the temperature less precisely. The A/C button will FLASH to indicate the presence of a fault.