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
The EMTC system has 2 system control inputs.
HVAC Module
The HVAC module integrates the temperature control, 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 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.
The HVAC module is not equipped with self-test capabilities.
Blower Motor Switch
The blower motor 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.
Control System Outputs
The EMTC system has 3 system outputs.
Blower Motor Resistor
The blower motor resistor:
- is located on the heater core and evaporator core housing near the blower motor.
- has 3 resistor elements mounted on the resistor board to provide 4 blower motor speeds.
- depending on the blower motor switch position, series resistance is added or bypassed in the blower motor circuit to decrease or increase blower motor speed.
Temperature Blend Door Actuator
The temperature blend door actuator:
- is located on the heater core and evaporator core housing.
- moves the temperature blend door on command from the HVAC module.
- contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the temperature blend door.
- applies a 5-volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the HVAC module and is matched with an expected wiper voltage value. The HVAC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected HVAC module wiper voltage value.
Airflow Mode Door Actuator
The airflow mode door actuator:
- uses a cam setup to direct system airflow to the vehicle interior as determined by the HVAC module.
- contains a reversible electric motor.
- contains a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the airflow mode doors.
- applies a 5-volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the HVAC module and is matched with an expected wiper voltage value. The HVAC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected HVAC module wiper voltage value.
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.
- contains a reversible electric motor.
- automatically stops when it reaches the full FRESH or full RECIRC position and does not report its position back to the HVAC module.
Electronic Automatic Temperature Control (EATC)
Two different Electronic Automatic Temperature Control (EATC) systems are available:
- Single-zone EATC (Fusion/Milan)
- Dual-zone EATC (MKZ)
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
- Temperature blend door position
- DEFROST/PANEL/FLOOR door position
- Air inlet door position
Control System Inputs
The EATC system has 4 control system inputs.
HVAC Module
The HVAC module:
- is located in the instrument panel.
- has a vacuum fluorescent display for displaying set temperature, airflow direction, blower speed and DTCs.
- utilizes an On-Board Diagnostic (OBD) feature to supply the technician with DTCs. These DTCs direct the technician to the inoperative component.
In-Vehicle Temperature Sensor
The in-vehicle temperature sensor operates in the following manner:
- A thermistor in the in-vehicle temperature sensor measures air temperature inside the passenger compartment.
- An aspirator hose and elbow is connected between the heater core and evaporator core housing and the in-vehicle temperature sensor.
- The aspirator hose and elbow uses airflow through the heater core and evaporator core housing to create a venturi-type suction in the in-vehicle temperature sensor.
- The suction draws in-vehicle air into the in-vehicle temperature sensor and across the thermistor.
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.
Blower Motor Speed Control
The blower speed control:
- is located on the heater core and evaporator core housing near the blower motor.
- varies the blower motor speed and is controlled by the HVAC module software.
Temperature Blend Door Actuator(s)
Single-zone EATC systems use one temperature blend door actuator. Dual-zone EATC systems use 2 separate temperature blend door actuators to control 2 separate temperature blend doors for the driver and passenger sides of the vehicle. The temperature blend door actuator(s):
- is/are located on the heater core and evaporator core housing.
- move the temperature blend door(s) on command from the HVAC module.
- each contain a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the temperature blend doors.
A 5-volt signal is applied to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the HVAC module and is matched with an expected wiper voltage value. The HVAC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected HVAC module wiper voltage value.
Airflow Mode Door Actuator
The mode door actuator:
- uses a cam setup to position the 2 airflow mode doors to direct system airflow to the vehicle interior as determined by the HVAC module settings.
- contains a reversible electric motor.
- contains a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the airflow mode doors.
A 5-volt signal is applied to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the HVAC module and is matched with an expected wiper voltage value. The HVAC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected HVAC module wiper voltage value.
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.
- contains a reversible electric motor.
- automatically stops when it reaches the full FRESH or full RECIRC position and does not report its position back to the HVAC module.