Air Temperature Sensors
The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors:
- Ambient Air Temperature Sensor
- Inside air temperature sensor assembly
- Sunload Sensor
- Upper air temperature sensor
- Lower air temperature sensor
A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +87.5°C (-40 to +190°F). The sensor signal varies between 0-5 volts.
The input of the duct air temperature sensors are different from the ambient and inside sensors. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease.
If the HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the inside air temperature sensor will be displayed on the scan tool. The default value for the duct air temperature sensors will not be displayed on the scan tool. The scan tool parameter for the duct air temperature sensors are the actual state of the signal circuit. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.
The ambient air temperature sensor mounts underhood and can be affected by city traffic, by idling, and by restarting a hot engine. Therefore, the HVAC control module filters the value of the ambient air temperature sensor for temperature display. The ambient air temperature value is updated under the following conditions:
| Condition | Display |
|---|---|
| When the HVAC module A/C and RECIRCULATION buttons are pressed simultaneously. | Updates temperature display instantly |
| At start up with the engine off less than 2 hours | Displays last stored temperature unless temperature has decreased. The outside air temperature reading is always instantly updated if ambient air temperature has decreased. |
| At start up with the engine off more than 2 hours | Displays actual outside temperature |
| Vehicle speed above 32 km/h (20 mph) for a minimum of 80 seconds | Updates temperature display at a slow filtered rate |
| Sensor ambient temperature reading is less than the last displayed value | Displays actual outside temperature |
| When the ambient air decreases. | Updates temperature display rapidly |