Tahoe 2WD V8-4.8L VIN V (2004)
Ambient Temperature Sensor / Switch HVAC: Description and Operation
AIR TEMPERATURE SENSORS
The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors:
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Ambient Air Temperature Sensor
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Inside Air Temperature Sensor Assembly
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Inside Air Temperature Sensor Assembly-Auxiliary
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Upper Left Air Temperature Sensor
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Upper Right Air Temperature Sensor
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Lower Left Air Temperature Sensor
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Lower Right Air Temperature Sensor
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Upper Air Temperature Sensor-Auxiliary
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Lower Air Temperature Sensor-Auxiliary
A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases.
The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40° to +101°C (-40° to +215°
F). The sensor signal varies between 0-5 volts.
The input of the duct air temperature sensors are different from the ambient and inside air temperature sensors. The HVAC control module converts the
signal to a range between 0-255 counts. As the air temperature increases the count value will decrease.
If the HVAC control module or auxiliary HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted
air temperature value. The default value for the ambient and inside air temperature sensors will be displayed on the scan tool. The default value for the
duct air temperature sensors will not be displayed on the scan tool. The scan tool parameter for the duct air temperature sensors are the actual state of the
signal circuit. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is
corrected.
The ambient air temperature sensor mounts underhood and can be affected by city traffic, by idling, and by restarting a hot engine. Therefore, the HVAC
control module filters the value of the ambient air temperature sensor for temperature display. The ambient air temperature value is updated under the
following condition
The scan tool has the ability to update the displayed ambient air temperature. To update the ambient air temperature display on the HVAC control
module, perform the following procedure:
1. Turn ON the ignition.
2. Simultaneously press the MODE, FRONT DEFROST and REAR DEFROST switches.
