Electronic Manual Temperature Control (EMTC)
Control Components
Electronic Manual Temperature Control (EMTC)
The HVAC module allows the vehicle occupants to select 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
Control System Inputs
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 serviced only as an assembly with the HVAC module.
The temperature control switch adjusts the discharge air temperature. Movement of the temperature knob from COOL (blue) to WARM (red) causes a corresponding movement of the temperature blend door. The position of the temperature blend door 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 serviced separately.
The airflow mode setting adjusts the discharge air outlet location. Movement of the airflow mode selector causes a corresponding movement of the airflow mode doors and determines the discharge air outlet location. The airflow mode selector is an integral part of the HVAC module and cannot be serviced separately.
The A/C request button determines A/C compressor operation, except when the airflow mode selector is in the OFF, MAX A/C, DEFROST or FLOOR/DEFROST mode. The A/C request button is an integral part of the HVAC module and cannot be serviced 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 serviced separately.
The rear defog button signals activation of the heated backlight. Under certain conditions, the heated backlight may be activated automatically by the PCM and Body Control Module (BCM). The rear defog button indicator may remain off during this time. The rear defog button is an integral part of the HVAC module and cannot be serviced separately.
Control System Outputs
The Electronic Manual Temperature Control (EMTC) system has 4 system outputs.
Blower Motor Speed
The HVAC module blower motor speed selector varies the blower motor ground circuit resistance by adding or bypassing series resistance in the blower motor resistor. Increased resistance lowers the blower motor speed, and lowered resistance increases 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 below 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 reports the position of the temperature blend door to the HVAC module. The HVAC module drives the temperature blend door actuator motor in whichever direction is necessary to move the temperature blend door to the position set by the vehicle occupants.
The temperature blend door actuator is mounted to the RH side of the heater core and evaporator core housing and can be serviced separately.
Airflow Mode Door Position
The airflow mode door actuator controls the airflow mode door actuating assembly to position the airflow mode doors on command from the HVAC module.
The airflow mode door actuator contains a reversible electric motor and potentiometer. The potentiometer circuit reports the position of the airflow mode doors to the HVAC module. The HVAC module drives the actuator motor in whichever direction is necessary to move the airflow mode doors to the position set by the vehicle occupants. The airflow mode door actuating assembly contains a cam and gear arrangement which transfers the rotation of the airflow mode door actuator to the individual airflow mode doors.
The airflow mode door actuating assembly is mounted to the LH side of the heater core and evaporator core housing and can be serviced separately. The airflow mode door actuator is mounted to the airflow mode door actuating assembly and can be serviced separately.
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. When the air inlet mode is switched, the airflow mode door actuator is driven by the HVAC module for 9 seconds, and will stall at the end of travel until the 9 second timer has expired.
The air inlet mode door actuator is mounted to the air inlet duct and can be accessed through the glove compartment. The air inlet mode door actuator can be serviced separately.