A educated guess I would have to say there is a problem with HVAC control module ! electronics you know ! But that's not the way to do things ! There could be codes stored in the module. The Chevy dealer my have a reflash bulletin for this problem . Then can reflash , reprogram the control module ! The first place to start is checking for codes in the HVAC module.
The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal.
Air Temperature Sensors
The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors:
Ambient Air Temperature Sensor
Inside Air Temperature Sensor Assembly
Inside Air Temperature Sensor Assembly-Auxiliary
Upper Left Air Temperature Sensor
Upper Right Air Temperature Sensor
Lower Left Air Temperature Sensor
Lower Right Air Temperature Sensor
Upper Air Temperature Sensor-Auxiliary
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 conditions: Or you can just buy a new control module an hope that it fixes it. $89.00 at www.partsgeek.com
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