Control Components
Control Components
Dual-Zone Electronic Automatic Temperature Control (EATC)
The HVAC module analyzes input from the following major sources:
- Temperature, airflow direction, blower, A/C and RECIRC selection (made by the vehicle occupants)
- In-vehicle temperature sensor
- Ambient temperature sensor
- Solar radiation sensor
- Vehicle speed
- Engine coolant temperature
Using these inputs, the HVAC module determines the correct conditions for the following outputs:
- A/C compressor operation
- Blower speed
- RH and LH temperature blend door positions
- Airflow mode door positions
- Air inlet mode door position
Control System Inputs
The dual-zone Electronic Automatic Temperature Control (EATC) system has 4 control system inputs.
HVAC Module - Without Navigation System
The HVAC module on vehicles not equipped with the navigation system provides an interface for the vehicle occupants to control the climate control system, or automatically controls the system in the AUTO mode. The Front Display Interface Module (FDIM) displays set temperature, airflow direction and blower speed.
The HVAC module is supplied as an assembly with the message center switches, traction control switch and hazard switch and is located at the front of the floor console below the Audio Control Module (ACM).
HVAC Module - With Navigation System
Vehicles equipped with the navigation system use a remote HVAC module that is separate from the control interface. The Front Controls Interface Module (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 module over the Medium Speed Controller Area Network (MS-CAN). The remote HVAC module controls the climate control system based on the FCIM selections or will automatically control the climate control system in the AUTO mode.
The remote HVAC module is located at the front of the floor console below the floor console front finish panel.
In-Vehicle Temperature Sensor
The in-vehicle temperature sensor contains a thermistor, which measures the in-vehicle air temperature and sends that reading to the HVAC module. An aspirator hose is connected between the heater core and evaporator core housing and the in-vehicle temperature sensor. The aspirator hose uses airflow through the heater core and evaporator core housing to create a Venturi-type suction in the hose to draw in-vehicle air through the in-vehicle temperature sensor (across the thermistor).
The in-vehicle temperature sensor is located on the instrument panel to the right of the steering column.
Sunload Sensor (Solar Radiation Sensor)
The solar radiation sensor supplies information to the dual-zone HVAC module indicating sunload. When sunload is detected, the information from the sensor is used to lower the A/C temperature output to compensate for radiant heat warming the vehicle interior and occupants.
Ambient Temperature Sensor
The ambient temperature sensor signal is received by the HVAC module and indicates the outside air temperature. The ambient temperature sensor is located in front of the radiator below the front bumper beam.
The ambient temperature sensor signal is not the sole factor considered by the HVAC module for the outside air temperature display. Therefore, the ambient temperature PID monitored with a scan tool may not exactly match the HVAC module display. For information regarding the outside air temperature display.
Control System Outputs
The EATC system has 4 control system outputs. When operating in AUTO mode, the control system outputs will be automatically adjusted by the HVAC module.
NOTE: Each of the 4 control system outputs may be overridden by the passenger if desired.
Blower Motor Speed
The blower motor speed control controls the blower motor speed by converting low power signals from the HVAC module to a high-current, variable ground feed for the blower motor. The HVAC module adjusts blower motor speed based on the difference between the in-vehicle temperature sensor signal and set temperature. A delay function is used to provide 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 will automatically shut down the blower motor. After shutdown, the blower motor speed control will attempt to restart every 120 seconds until the blower motor can be safely operated.
The blower motor speed control is located on the heater core and evaporator core housing near the blower motor.
Temperature Blend Door Position
The dual-zone EATC system uses 2 temperature blend door actuators to control 2 separate temperature blend doors. The temperature blend doors independently vary the LH side 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 module from the contact wiper indicates the position of the temperature blend door. The HVAC 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 module based on the set temperature, in-vehicle temperature, ambient temperature and sunload.
The LH temperature blend door actuator is located on the heater core and evaporator core housing near the accelerator pedal. The RH temperature blend door actuator is located on the heater core and evaporator core housing to the left of the glove compartment.
Airflow Mode Door Position
The airflow mode door actuator uses a cam and lever assembly to position the airflow mode doors on command from the HVAC module. The mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC module to monitor the position of the airflow mode doors. 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 module from the contact wiper indicates the position of the airflow mode doors. The HVAC module powers the actuator motor to move the airflow mode doors to the desired position. The HVAC module determines the desired airflow mode door position based on the calculated outlet temperature.
The airflow (defrost/panel/floor) mode door actuator is located on the heater core and evaporator core housing to the right of the steering column.
Air Inlet Mode Door Position
The air inlet mode door actuator moves the air inlet door between the fresh and RECIRC positions on command from the HVAC module. The airflow mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC module to monitor the position of the air inlet 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 module from the contact wiper indicates the position of the air inlet mode door. The HVAC module powers the actuator motor to move the air inlet mode door to the desired position. The HVAC module determines the desired air inlet mode door position based on the calculated outlet temperature.
The air inlet mode door actuator is located on the air inlet duct and can be accessed through the glove compartment opening with the glove compartment lowered.