Cabin Humidity And Temperature Sensor

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Fig 1: Cabin Humidity And Temperature Sensor

Courtesy of JAGUAR CARS, INC.

The cabin humidity and temperature sensor is installed behind a grill on the drivers side of the instrument panel. The temperature inside the cabin is measured by a negative temperature coefficient (NTC) thermistor. A motor within the sensor assembly draws cabin air in through the grill and over the thermistor. The motor is provided a battery voltage feed by a relay located within the central junction box (CJB).

Humidity inside the cabin is measured by a sensor element made up of film capacitors on different substrates. The dielectric is a polymer which absorbs or releases water proportional to the relative humidity of the air being drawn through the sensor and thus changes the capacitance of the capacitor. For protection, the sensor element is contained in a nylon mesh cover.

Humidity within the cabin is controlled by raising and lowering the evaporator temperature. An increase in evaporator temperature increases the moisture content in the air entering the cabin. Lowering the evaporator temperature reduces the moisture content in the air entering the cabin.