Electronic Manual Temperature Control (EMTC)

Control Components

The Electronic Manual Temperature Control (EMTC) system control 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.

Electronic Manual Temperature Control (EMTC)

Control System Inputs

HVAC Module

The EMTC (Electronic Manual Temperature Control) system uses 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 (Front Controls Interface Module) 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 (Front Controls Interface Module) selections.

The HVAC module is mounted to the instrument panel support behind the FCIM (Front Controls Interface Module).

Control System Outputs

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 blower speed selector position. 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.

Airflow Mode Door Position

The climate control system uses 2 electric airflow mode door actuators to control the airflow mode doors.

The panel/defrost airflow mode door actuator uses a cam and lever assembly to position the panel and defrost airflow mode doors on command from the HVAC module. The panel/defrost mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC module to monitor the position of the panel and defrost 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 floor airflow mode door actuator positions the floor mode door on command from the HVAC module. The floor mode door actuator is driven to, and will automatically stop at, the full open or full closed position and does not require a feedback circuit to report its position to the HVAC module. 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 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.

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.

The temperature blend door actuator is located on the heater core and evaporator core housing to the left of the glove compartment.