Ambient Temperature Sensor / Switch HVAC: Description and Operation

AIR TEMPERATURE SENSORS




The air temperature sensors are 2 wire negative temperature co-efficient thermistors. The vehicle uses the following air temperature sensors:
- Ambient
- Inside
- Upper right
- Upper left
- Lower right
- Lower left

The upper and lower duct sensors are divided into left and right zone operation. The left side upper and lower duct sensors will only effect the operation of the left air temperature actuator and the right side upper and lower duct sensors will only effect the operation of the right air temperature actuator. The duct sensors are used to measure the temperature of the air exiting the ducts. The sensors operate within a temperature range between -6.5°C (20.3°F) to 57.5°C (135.5°F). When temperature increases the sensor signal decreases. The HVAC control module converts the 0-5 volt sensor signal to a range between 0-255 counts. If the HVAC control module (IPM) detects that one of the duct temperatures must change, the HVAC control module (IPM) will adjust the appropriate air temperature actuator. The following list shows the duct sensors that are monitored by the HVAC control module in each mode position.

If the HVAC control module (IPM) detects a malfunctioning sensor, the HVAC system will only malfunction when the sensor is monitored. The inside temperature sensor operates within a temperature range between -6.5°C (20.3°F) to 57.5°C (135.5°F). If the sensor is shorted to ground, the system will operate in the maximum cooling mode. If the sensor is shorted to voltage or open, the system will operate in the maximum heating mode. The ambient sensor operates within a temperature range between -30°C(-22°F) to 51°C (123.8°F). If the HVAC control module (IPM) has determined that the ambient air temperature sensor has failed, the IPM shall display "--" in place of the ambient air temperature. If the sensor is shorted to ground, the system will operate in the maximum cooling mode. If the sensor is shorted to voltage or open, the system will operate in the maximum heating mode. If the engine coolant temperature is not more than 28°C (50°F) above the sensor reading, or if the engine has not been started in two hours, then the actual ambient air temperature sensor reading is displayed. The ambient air temperature displayed may be allowed to increase after 80 seconds as long as the vehicle speed is greater than 32 km/h (20 mph), but only at a slow, filtered rate. If the sensor reading is ever less than the displayed value or if the vehicle speed is 72 km/h (45 mph) or greater, then the ambient air temperature changes are displayed as rapidly as possible. The (IPM) displays the ambient air temperature.