Ambient Temperature Sensor / Switch HVAC: Description and Operation
AIR TEMPERATUREINSIDE AIR TEMPERATURE SENSOR
Replacement of the inside air temperature sensor means replacing the HVAC control module. The inside air temperature sensor is an integral part of the HVAC control module. The HVAC control module monitors the passenger compartment inside air temperature through an inside air temperature sensor. When the air is cold, the sensor resistance and the signal voltage are high. When the air is warm, the sensor resistance and the signal voltage are low. The HVAC control module requests A/C compressor clutch engagement and controls the air temperature actuator door positions in order to maintain the selected air temperature. The HVAC control module sends out a 5-volt reference signal to the inside air temperature sensor over the 5-volt reference circuit. A thermistor varies the reference voltage back to the HVAC control module through the low reference circuit.
AMBIENT AIR TEMPERATURE SENSOR
The ambient air temperature sensor is a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors:
- Ambient
- Inside
A 5-voltreference and signal circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases.
The sensor operates within a temperature range of -40°C (-40°F) to 60°C (140°F). The HVAC control module receives a class 2 message from the instrument panel cluster (IPC). The ambient air temperature sensor is mounted in the forward engine area of the vehicle. In this position, it is exposed to the airflow through the grill before it reaches the radiators. The sensor signal varies between 0 to 5 volts. The HVAC control module converts the signal to a working temperature range.
If the HVAC control module detects a faulty class 2 signal, then the control module software will use a defaulted air temperature value.
The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the system is fixed.
The ambient air temperature is updated and displayed under the given conditions.