S15/T15 Sonoma P/U 2WD L4-2.2L VIN 5 Flex Fuel (2001)
Cabin Temperature Sensor / Switch: Description and Operation
TEMPERATURE SENSORS
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 assembly housing continually draws passenger compartment air over the sensor. The fan receives
power from the instrument panel fuse block on the ignition 3 voltage circuit and splice pack. 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. That varied voltage provides a signal to the software inside the HVAC control module. As the air
temperature increases, resistance decreases. Ground is provided by the low reference circuit.
The lower 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 air temperature sensor over the lower discharge 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.
Ground is provided by the low reference circuit.
The upper 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 air temperature sensor over the upper discharge 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. Ground is
provided by the low reference circuit.
The ambient air temperature sensor provides the HVAC control module software with the temperature outside the vehicle. 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. Ground is provided by the low reference circuit.
Since the sensor is mounted behind the grille and can be affected by city traffic, idling, and hot engine restarts, the ambient air temperature sensor could
give a false temperature reading. If the vehicle has been turned off for 1 hour or longer, and the ambient air temperature has cooled, the HVAC control
module will slowly update. Updates to the HVAC control module will begin once the vehicle travels over 40 km/h (25 mph). The module will update
faster as vehicle speed increases, up to 105 km/h (65 mph). If an immediate update is needed, disconnect the vehicle battery.
