Ambient Temperature Sensor / Switch HVAC: Description and Operation

Temperature Sensor, External Air (286)

Location
Temperature sensor, external air (286)







Principal use
Used to show the external temperature in SID. The value is also sent out on the bus and used by other systems.

Type
The sensor consists of an NTC resistor which is encapsulated in a plastic casing. The outside is fitted with three snap fasteners for mounting, and a contact unit.

Connection











One pin is grounded internally in the control module and the other supplied with 5V via a resistor of 6.8 kohms built into the control module. The characteristics of the NTC resistor mean that the resistance falls as the temperature rises. This means that the voltage measured over the resistor will fall at the same time as the temperature rises. The power supply from the sensor is A/D-converted and then available in digital form. The digital voltage is then converted to temperature and stored in the control module working memory. A voltage value of almost 0 or 5V is interpreted as a fault in the circuit.