Control Components

Control Components

Two climate control systems are available:

- Electronic Manual Temperature Control (EMTC)
- Dual-zone Electronic Automatic Temperature Control (EATC)

Refer to the appropriate heading below for information concerning each system.

Electronic Manual Temperature Control (EMTC)

NOTE: EMTC is not available on hybrid vehicles.

NOTE: When installing a new HVAC module on vehicles equipped with EMTC, the Programmable Module Installation (PMI) procedure must be carried out to configure the new module to the vehicle. Refer to Module Configuration Programmable Module Installation (PMI).

The HVAC module selections include the following:

- Air inlet source (outside or recirculated)
- Blower motor speed
- Discharge air temperature (temperature blend)
- Discharge air location (defrost, panel, floor, panel/floor, defrost/floor)
- A/C compressor operation
- Rear window defroster operation
- Heated seat operation (if equipped)

Control System Inputs

The temperature control selector 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 discharge air temperature that the air distribution system will maintain. The temperature control selector is an integral part of the HVAC module and cannot be installed separately. The temperature selector knob is removable and can 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 airflow mode selector is in the OFF, MAX A/C or DEFROST mode. 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 recirculated air request button is an integral part of the HVAC module and cannot be installed separately.

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.

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 switch knob is removable and can be installed separately.

Control System Outputs

The EMTC system has 4 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 behind the glove compartment.

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 drives the actuator motor in whichever direction is necessary to make the actuator contact wiper voltage agree with the expected HVAC module value. The expected value is set by the vehicle occupants using the temperature selector knob.

The temperature blend door actuator is mounted to the top of the heater core and evaporator core housing.

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 expected HVAC value is set by the vehicle occupants using the mode selector buttons.

The airflow mode door actuator is mounted to the plenum chamber to the right of the accelerator pedal.

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 airflow mode door does not stop at any point between the RECIRC or fresh air inlet position.

The air inlet mode door actuator is mounted to dash panel side of the air inlet duct.

Electronic Automatic Temperature Control (EATC)

The HVAC module analyzes input from the following major sources:

- Temperature, airflow mode, blower, A/C and RECIRC selection (made by the vehicle occupants)
- In-vehicle temperature sensor (non-hybrid only)
- In-vehicle temperature and humidity sensor (hybrid only)
- Ambient temperature sensor
- Sunload sensor (solar radiation sensor)
- Evaporator discharge air temperature sensor
- Vehicle speed
- Engine Coolant Temperature (ECT)

Using these inputs, the HVAC module determines the correct conditions for the following outputs:

- A/C compressor ON/OFF request
- Blower motor speed
- Temperature blend door position
- Airflow mode door position
- Air inlet door position

Control System Inputs

The dual-zone EATC system has 4 control system inputs.

HVAC Module

The HVAC module provides an interface for the vehicle occupants to control the climate control system, or automatically controls the climate control system in the AUTO mode. The HVAC module uses the Front Display Interface Module (FDIM) for displaying set temperature, airflow direction, blower speed and DTCs. An On-Board Diagnostic (OBD) feature is incorporated to supply the technician with DTCs. These DTCs help direct the technician to the inoperative component.

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 to draw in vehicle air through the in-vehicle temperature sensor (across the thermistor).

The in-vehicle temperature sensor is mounted to the RH lower portion of the instrument cluster finish panel.

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. An aspirator hose and elbow is connected between the heater core and evaporator core housing and the in-vehicle temperature and humidity sensor. The aspirator hose uses airflow from the heater core and evaporator core housing air stream to create a Venturi-type suction to draw in vehicle air through the in-vehicle temperature sensor and across the thermistors.

The in-vehicle temperature and humidity sensor is mounted to the RH lower portion of the instrument cluster finish panel.

Sunload Sensor (Solar Radiation Sensor)

The solar radiation sensor supplies information to the HVAC module indicating sunload strength, and (to an extent) direction. The solar radiation sensor is located on the center of the instrument panel at the base of the windshield.

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 bottom of the 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 HVAC module outside air temperature display, refer to Climate Control System - General Information and Diagnostics Climate Control System - General Information and Diagnostics.

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. A delay function is used to provide a gradual increase or decrease in blower motor speed under all conditions.

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 return circuit is connected to a contact wiper, which is driven along the variable resistor by the actuator shaft. The signal returned to the HVAC module from the contact wiper indicates the position of the temperature blend door. The HVAC module drives the actuator motor in whichever direction is necessary to make the actuator contact wiper voltage agree with the expected HVAC module contact wiper voltage value, as determined by the control algorithm.

The LH temperature blend door actuator is mounted to the bottom of the heater core and evaporator core housing. The RH temperature blend door actuator is mounted to the top of the heater core and evaporator core housing.

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 drives the actuator motor in whichever direction is necessary to make the actuator contact wiper voltage agree with the expected contact wiper voltage value, as determined by the control algorithm.

The airflow mode door actuator is mounted to the plenum chamber to the right of the accelerator pedal.

Air Inlet Mode Door Actuator

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 airflow mode door on non-hybrid vehicles does not stop at any point between the RECIRC or fresh air inlet position. On hybrid vehicles only, the air inlet door may stop in a mid-position if required for increased cooling performance as determined by the HVAC module.

The air inlet mode door actuator is mounted to dash panel side of the air inlet duct.