Control Components
Control Components
Electronic Manual Temperature Control (EMTC)
The Electronic Manual Temperature Control (EMTC) 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
HVAC Module
The HVAC module integrates the temperature control, blower motor switch, airflow mode selection, A/C request button, recirculated air request button and rear defog switch into a single unit.
The temperature control switch setting determines air temperature. Movement of the temperature display from COOL (blue) to WARM (red) causes a corresponding movement of the temperature blend door and determines the air discharge temperature that the air distribution system will maintain. The temperature control switch is an integral part of the HVAC module and cannot be installed separately.
The blower motor speed switch is mounted in the HVAC module and controls blower motor speed by adding or bypassing resistors in the blower motor resistor in all modes except OFF. The blower motor speed switch is an integral part of the HVAC module and cannot be installed separately.
The airflow mode setting determines air discharge location. Depressing each airflow mode selector button causes a corresponding movement of the airflow mode doors and determines the air discharge location. The airflow mode selector buttons are an integral part of the HVAC module and cannot be installed separately.
The A/C request button determines A/C compressor operation, except when the function selected is OFF, MAX or DEFROST. The A/C request button is an integral part of the HVAC module and cannot be installed separately.
The recirculated air request button can select recirculated air in any mode except DEFROST, and fresh air in any mode except MAX A/C or OFF.
The rear defog button signals activation of the heated backlight. The rear defog button is an integral part of the HVAC module and cannot be installed separately.
Control System Outputs
The EMTC system has 3 system outputs.
Blower Motor Speed
The blower motor speed switch varies the blower motor ground circuit resistance by adding or bypassing series resistance in the blower motor resistor. Increased resistance will lower the blower motor speed, and lowered resistance will increase blower motor speed. When the blower motor is in the HI (4) position, the blower motor resistor is bypassed.
The blower motor resistor is located on the heater core and evaporator core housing near the blower motor.
Temperature Blend Door Position
The temperature blend door actuator moves the temperature blend door on command from the HVAC module.
The temperature blend door actuator contains 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 motor to move the temperature blend door to the desired position. The desired position is set by the vehicle occupants using the temperature selector knob.
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 desired position is set by the vehicle occupants using the mode selector buttons.
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 air inlet mode door actuator is driven to, and will automatically stop at, the full RECIRC or full fresh air inlet position and does not require a potentiometer circuit to monitor its position. The air inlet mode door does not stop at any point between the RECIRC or fresh air inlet position.
The air inlet mode door actuator is located on the air inlet duct near the RH cowl side panel.
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 (non-hybrid)
- In-vehicle temperature and humidity sensor (hybrid)
- Ambient air temperature sensor
- Solar radiation sensor (sunload sensor)
- Vehicle speed
- Engine coolant temperature
- Occupant Classification Sensor (OCS) (hybrid only)
Using these inputs, the HVAC module determines the correct conditions for the following outputs:
- A/C compressor operation
- Blower motor speed
- RH and LH temperature blend door positions
- DEFROST/PANEL/FLOOR airflow mode door position
- Air inlet mode door position
Control System Inputs
The 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 mounted to the center instrument panel finish panel below the Front Controls Interface Module (FCIM).
HVAC Module - With Navigation System
Vehicles equipped with the navigation system use a remote HVAC 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 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 HVAC module is mounted to the instrument panel support behind the FCIM.
In-Vehicle Temperature Sensor - Non-Hybrid
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 mounted to the instrument panel to the right of the steering column with the aspirator hose connected to the heater core and evaporator core housing near the LH temperature blend door actuator.
In-Vehicle Temperature and Humidity Sensor - Hybrid
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 module. The in-vehicle temperature sensor has an integral electric fan within the sensor that draws in-vehicle air across the thermistors.
The in-vehicle temperature and humidity sensor is mounted to the instrument panel to the right of the steering column.
Solar Radiation Sensor (Sunload Sensor)
The solar radiation sensor supplies information to the HVAC module indicating sunload.
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 on the radiator support.
Control System Outputs
The EATC system has 3 control system outputs.
NOTE: For the passenger side temperature setting on hybrid vehicles equipped with a dual-zone Electronic Automatic Temperature Control (EATC) and a Front Controls Interface Module (FCIM) built on or after 4/08/2009 to be functional, a passenger must be seated in the front passenger seat. If the front passenger seat is not occupied, the HVAC module will control the system based only on the driver side temperature setting. The HVAC module receives a Medium Speed Controller Area Network (MS-CAN) signal from the FCIM to indicate if the front passenger seat is occupied.
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 is located on the heater core and evaporator core housing near the blower motor.
Temperature Blend Door Positions
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 mode door actuator is located on the heater core and evaporator core housing to the right of the accelerator pedal.
Air Inlet Mode Door Actuator - Non-hybrid
The air inlet mode door actuator moves the air inlet door between the fresh and RECIRC positions on command from the HVAC module. The air inlet mode door actuator is driven to, and will automatically stop at, the full RECIRC or full fresh air inlet position and does not require a potentiometer circuit to monitor its position. The air inlet mode door does not stop at any point between the RECIRC or fresh air inlet position.
The air inlet mode door actuator is located on the air inlet duct near the RH cowl side panel.
Air Inlet Mode Door Actuator - Hybrid
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 near the RH cowl side panel.