Dual Automatic Temperature Control (DATC)
The DATC components are used to select:
- air inlet source (outside or recirculated).
- blower motor speed.
- discharge air temperature (temperature blend).
- discharge air location (defrost, panel, floor).
- A/C compressor operation.
Control System Inputs
The DATC system has 4 control system inputs.
HVAC Control Module
The DATC system uses a remote HVAC control module that is separate from the control interface. The FCIM provides the interface for the vehicle occupants to control the climate control system. When selections are made, the FCIM communicates the selections to the HVAC control module over the vehicle module communication network. The remote HVAC control module controls the climate control system based on the FCIM selections or automatically controls the climate control system in the AUTO mode.
In-Vehicle Temperature and Humidity Sensor
The in-vehicle temperature and humidity sensor contains 2 thermistors which separately measure the in-vehicle air temperature and humidity and send those readings to the HVAC control module. The in-vehicle temperature and humidity sensor has an electric fan within the sensor that draws in-vehicle air across the thermistors.
Autolamp/Sunload Sensor (Light Sensor)
The autolamp/sunload sensor supplies information to the DATC HVAC control module to lower the A/C temperature output in the vehicle's cabin, cooling the vehicle interior and occupants.
The autolamp/sunload sensor is also used by the exterior lighting system for autolamp operation. For removal and installation of the autolamp/sunload sensor, refer to Light Sensor in EXTERIOR LIGHTING SYSTEM .
AAT Sensor
The AAT sensor signal is received by the HVAC control module over the vehicle module communication network from the PCM.
For information regarding the outside air temperature display, refer to INFORMATION CENTER - INSTRUMENTATION, MESSAGE CENTER, AND WARNING CHIMES .
Control System Outputs
The DATC system has 4 control system outputs. When operating in AUTO mode, the control system outputs are automatically adjusted by the HVAC control module.
Blower Motor Speed Control
The HVAC control module controls the blower speed by sending a PWM signal to the blower motor speed control. The blower motor speed control provides variable ground feed for the blower motor to control the speed. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.
The blower motor speed control has internal temperature and surge protection. In the event of excessive blower motor supply voltage or current draw, or if the blower motor speed control temperature climbs considerably due to a failure event (such as a seized or partially-seized blower motor), the blower motor speed control automatically shuts down the blower motor. After shutdown, the blower motor speed control attempts to restart every 120 seconds until the blower motor can be safely operated.
Temperature Blend Door Position
The DATC system uses 2 temperature blend door actuators to control 2 separate temperature blend doors. The temperature blend doors independently vary the LH and RH side temperature settings, as desired. The temperature blend door actuators each contain a reversible electric motor and a potentiometer. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a contact wiper, which is driven along the variable resistor by the actuator shaft. The signal to the HVAC control module from the contact wiper indicates the position of the temperature blend door. The HVAC control module powers the actuator motors to move the temperature blend doors to the desired positions. The desired temperature blend door positions are calculated by the HVAC control module based on the set temperature, in-vehicle temperature, ambient air temperature and sunload.
Defrost/Panel/Floor Mode Door Position
Airflow through the HVAC plenum is controlled by the defrost/panel/floor mode door actuator. The defrost/panel/floor mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the defrost/panel/floor mode door. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a contact wiper, which is driven along the variable resistor by the actuator shaft. The signal to the HVAC control module from the contact wiper indicates the position of the defrost/panel/floor mode door. The HVAC control module powers the actuator motor to move the defrost/panel/floor mode door to the desired position. The desired position is set by the vehicle occupants using the mode selector buttons.
Air Inlet Mode Door Position
The air inlet mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the air inlet mode door. The HVAC control module adjusts the air inlet door depending on the humidity measured by the in-vehicle temperature and humidity sensor. If the vehicle cabin becomes too humid and recirculated air is not selected, the HVAC control module adjusts the air inlet door to allow more recirculated air. When the humidity level drops, it adjusts back to fresh air.