Temperature Sensors

The automatic system uses multiple sensors to achieve and maintain the desired temperature. The inside air temperature sensor provides the HVAC control module software with the inside air temperature from the inside air temperature sensor assembly. A fan located internally to the inside air temperature sensor housing continually draws passenger compartment air over the sensor. The fan receives power from the rear fuse block on the ignition 3 voltage circuit. Ground is provided by the dash integration module on the inside air temperature sensor assembly control circuit.

A 5-volt reference signal is sent from the HVAC control module to the inside air temperature sensor over the inside air temperature sensor input circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. As the air temperature increases, resistance decreases. Remaining voltage from the inside air temperature sensor is sent back to the HVAC control module ground through the sensor return circuit.

The lower left air temperature sensor provides the HVAC control module software with the temperature of the air exiting from the left closeout/insulator panel. A 5-volt reference signal is sent from the HVAC control module to the lower left air temperature sensor over the lower left air temperature sensor input circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. Remaining voltage from the lower left air temperature sensor is sent back to the HVAC control module ground through the sensor return circuit.

The lower right air temperature sensor provides the HVAC control module software with the temperature of the air exiting from the right closeout/insulator panel for passenger side temperature offset. A 5-volt reference signal is sent from the HVAC control module to the lower right air temperature sensor over the lower right air temperature sensor input circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. Remaining voltage from the lower right air temperature sensor is sent back to the HVAC control module ground through the sensor return circuit.

The upper left air temperature sensor provides the HVAC control module software with the temperature of the air exiting from the left A/C duct. A 5-volt reference signal is sent from the HVAC control module to the upper left air temperature sensor over the upper left air temperature sensor input circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. Remaining voltage from the upper left air temperature sensor is sent back to the HVAC control module ground through the sensor return circuit.

The upper right air temperature sensor provides the HVAC control module software with the temperature of the air exiting from the right A/C duct for passenger side temperature offset. A 5-volt reference signal is sent from the HVAC control module to the upper right air temperature sensor over the upper right air temperature sensor input circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. Remaining voltage from the upper right air temperature sensor is sent back to the HVAC control module ground through the sensor return circuit.

The auxiliary air temperature sensor provides the HVAC control module software with the temperature of the air in the ductwork for back seat passenger temperature offset. A 5-volt reference signal is sent from the HVAC control module to the auxiliary air temperature sensor over the auxiliary air temperature sensor input circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. Remaining voltage from the auxiliary air temperature sensor is sent back to the HVAC control module ground through the sensor return circuit.

The ambient air temperature sensor provides the HVAC control module software with the temperature of the air outside the vehicle and displays that temperature on the HVAC control module. A 5-volt reference signal is sent from the HVAC control module to the ambient air temperature sensor over the ambient air temperature sensor input circuit. A thermistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. As the air temperature increases, resistance decreases. Remaining voltage from the ambient air temperature sensor is sent back to the HVAC control module ground through the sensor return circuit.

Since the sensor is mounted underhood it can be affected by city traffic, idling, and hot engine restarts. A temperature memory feature is used in the HVAC control module ambient air temperature programming to help provide greater accuracy under engine restart conditions. If the engine coolant temperature is not more than 10°C (18°F) above the ambient air temperature sensor reading, or if the engine has not been started in two hours, then the actual ambient air temperature sensor reading is displayed. However, if the engine coolant is more than 10°C (18°F) above the sensor reading, the memorized ambient air temperature is displayed. This is the last displayed temperature sensed when the engine was operating. At vehicle speeds greater than 16 km/h (10 mph), the ambient air temperature displayed may be allowed to increase, but only after a built-in 300-second time delay which allows for outside air to cool the sensor. The time delay starts when vehicle speed reaches or maintains at least 16 km/h (10 mph). If the sensor reading is ever less than the displayed value, then the ambient air temperature changes are displayed as rapidly as possible.