Temperature Sensor

When the vehicle operator determines what temperature is desired, the automatic system uses multiple sensors to achieve and maintain the desired temperature. The HVAC control module software receives an input of 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 ground 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 signal circuit. A thermister inside the sensor varies the voltage. As temperature increases, resistance decreases. 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 low reference circuit.

The lower left air temperature sensor provides the HVAC control module software with the temperature of the heat in the ductwork. 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 signal circuit. A thermister 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 low reference circuit.

The lower right air temperature sensor provides the HVAC control module software with the temperature of the heat in the ductwork 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 signal circuit. A thermister 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 low reference circuit.

The upper left air temperature sensor provides the HVAC control module software with the temperature of the A/C in the ductwork. 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 signal circuit. A thermister 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 low reference circuit.

The upper right air temperature sensor provides the HVAC control module software with the temperature of the A/C in the ductwork 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 signal circuit. A thermister 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 low reference circuit.

The ambient air temperature sensor provides the HVAC control module software with the temperature outside the vehicle and displays that temperature on the HVAC control module. As temperature increases, resistance decreases. A 5-volt reference signal is sent from the HVAC control module to the ambient air temperature sensor over the ambient air temperature sensor signal circuit. A thermister 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 low reference circuit.

Since the sensor is mounted underhood and can be affected by city traffic, idling, and hot engine restarts, the ambient air temperature sensor could give a false temperature reading. 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 less than 28°C (50°F) above outside air ambient temperature, 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 28°C (50°F) above the sensor reading, the memorized ambient air temperature is displayed. This is the last displayed temperature sensed when the vehicle was operating. At vehicle speeds greater than 32 km/h (20 mph), the ambient air temperature display may be allowed to increase, but only after a built-in 80-second time delay which allows for outside air to cool the sensor. The time delay starts when vehicle speed reaches or maintains at least 32 km/h (20 mph). 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.