Air Temperature Description and Operation - part 2
Auxiliary Air Temperature Actuator
The auxiliary air temperature actuator is a 5-wire bi-directional electric motor thatincorporates a feedback potentiometer. Ignition-3 voltage, low reference, control,5-volt reference and position signal circuits enable the actuator to operate. Thecontrol circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement.When the actuator is at rest, the control circuit value is 2.5-volts. A 0 or 5-voltcontrolsignal commands the actuator movement in opposite directions. When the actuator shaftrotates, the potentiometers adjustable contact changes the door position signal between0–5-volts. The auxiliary HVAC control module uses a range of 0–255-counts to indexthe actuator position. The door position signal voltage is converted to a 0–255-countrange. When the module sets a commanded, or targeted, value, the control signalis changed to either 0 or 5-volts depending upon the direction that the actuator needsto rotate to reach the commanded value. As the actuator shaft rotates the changingposition signal is sent to the module. Once the position signal and the commandedvalue are the same, the module changes the control signal to 2.5-volts.
Air Temperature Sensor
The air temperature sensors are a 2-wire negative temperature co-efficient thermistor.The vehicle uses the following air temperature sensors:Ambient Air Temperature SensorInside Air Temperature Sensor AssemblyUpper Left Air Temperature SensorUpper Right Air Temperature SensorLower Left Air Temperature SensorLower Right Air Temperature SensorUpper Air Temperature Sensor – AuxiliaryLower Air Temperature Sensor – Auxiliary
A signal and low reference circuit enables the sensor to operate. As the air temperaturesurrounding the sensor increases, the sensor resistance decreases. The sensor signalvoltage decreases as the resistance decreases. The sensor operates within a temperaturerange 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 insideair temperature sensors. The HVAC control module converts the signal to a range between0–255-counts. As the air temperature increases the count value will decrease. If theHVAC control module or auxiliary HVAC control module detects a malfunctioning sensor,then the control module software will use a defaulted air temperature value. The defaultvalue for the ambient and inside air temperature sensors will be displayed on thescan tool. The default value for the duct air temperature sensors will not be displayedon the scan tool. The scan tool parameter for the duct air temperature sensors arethe actual state of the signal circuit. The default action ensures that the HVAC systemcan adjust the inside air temperature near the desired temperature until the conditionis corrected.