Control Components

ELECTRONIC MANUAL TEMPERATURE CONTROL

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.

EMTC Module (Climate Control Assembly)
The climate control assembly integrates the temperature control, mode function selection, A/C request button, recirculated air request button and rear defog button into a single unit.

The temperature control switch setting determines air temperature. Movement of the temperature knob 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 climate control assembly and cannot be installed separately.

The A/C request button determines A/C compressor operation, except when the function selected is OFF, MAX A/C, DEFROST, or FLOOR/DEFROST. The A/C request button an integral part of the climate control assembly and cannot be installed separately.

The recirculated air request button can select recirculated air in any mode except MAX A/C, OFF or DEFROST.

The rear defog button (if equipped) signals activation of the heated backlight and heated exterior rear view mirrors. The rear defog button is an integral part of the climate control assembly and cannot be installed separately.

The heated mirror button (if equipped) signals activation of the heated exterior rear view mirrors. The heated mirror button is an integral part of the climate control assembly and cannot be installed separately.

The EMTC module is not equipped with self-test capabilities.

Blower Motor Switch
The blower motor switch is mounted in the climate control assembly and controls blower motor speed by adding or bypassing resistors in the blower motor resistor in all function selector switch positions except OFF.

Control System Outputs
The EMTC system has 3 system outputs.

Blower Motor Resistor
The blower motor resistor adjusts the blower motor speed based on the blower motor switch setting. The blower motor resistor contains 3 resistor coils in series. The end of each resistor coil is wired to a setting in the blower motor switch. Voltage from the blower motor relay is available at the blower motor at all times when the blower selector is in an ON position, and then continues to the blower motor resistor. The blower motor switch will allow a path to ground with the addition of 1, 2 or 3 coils in the blower motor resistor to the circuit. When the blower motor switch is in the MED HI position, the blower motor switch will add a path to ground through 1 coil in the blower motor resistor. When the blower motor switch is in the MED LO position, the blower motor switch will add a path to ground through 2 coils (in series) in the blower motor resistor. When the blower motor switch is in the LO position, the blower motor switch will add a path to ground through 3 coils (in series) in the blower motor resistor. When the blower motor switch is in the HI position, the blower motor resistor is bypassed.

Temperature Blend Door Actuator
An electric temperature blend door actuator is used to position the temperature blend door. The temperature blend door actuator contains a reversible electric motor to position the temperature blend door. A potentiometer is installed in the actuator to allow the EMTC module to monitor the position of the temperature blend 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 return circuit is connected to a wiper which is driven along the variable resistor by the actuator shaft. The signal returned to the EMTC module from the wiper indicates the position of the temperature blend door.

Mode Door Actuators
Electric mode door actuators are used to position the 3 airflow mode doors. The 3 mode door actuators each contain a reversible electric motor to position the airflow mode door. A potentiometer is installed in the floor/defrost door and panel door actuators to allow the EMTC 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 return circuit is connected to a wiper which is driven along the variable resistor by the actuator shaft. The signal returned to the EMTC module from the wiper indicates the position of the airflow mode door. The air inlet mode door actuator is driven to the full RECIRC or full FRESH air inlet position, and does not require a potentiometer circuit to monitor it's position.

ELECTRONIC AUTOMATIC TEMPERATURE CONTROL

The electronic automatic temperature control (EATC) module analyzes input from the following major sources:
- Temperature, airflow direction and blower selection (made by the vehicle occupants)
- In-vehicle temperature
- Ambient temperature
- Sunload
- Vehicle speed
- Engine coolant temperature

Using these inputs, the EATC module determines the correct conditions for the following outputs:
- A/C compressor operation
- Blower speed
- Temperature blend door position
- Panel door position
- Floor/defrost door position
- Air inlet door position

Control System Inputs
The EATC system has 5 control system inputs.

EATC Module (Climate Control Assembly)
The EATC 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 EATC module has a vacuum fluorescent display for displaying set temperature, airflow direction, blower speed and diagnostic trouble codes (DTCs). An on-board diagnostic (OBD) feature is incorporated to supply the technician with diagnostic trouble codes (DTCs). These DTCs help direct the technician to the inoperative component.

The EATC module display will switch between Celsius and Fahrenheit when the instrument cluster display is toggled.

Steering Wheel Audio/Climate Control Switch
The steering wheel audio/climate control switch allows the driver to adjust the passenger compartment temperature setting and manually override the blower motor speed setting.

In-Vehicle Temperature Sensor
An in-vehicle temperature sensor is used by the EATC module to measure air temperature inside the passenger compartment. An aspirator hose and elbow is connected between the heater core housing and the in-vehicle temperature sensor. Airflow through the heater core and evaporator core housing causes a venturi-type suction through the aspirator hose which draws passenger compartment air across the thermistor in the in-vehicle temperature sensor.

Solar Radiation Sensor (Sunload Sensor)
The solar radiation sensor supplies information to the EATC module indicating sunload.

Ambient Temperature Sensor
The ambient temperature sensor signal is received by the instrument cluster module which communicates it to the EATC module via the vehicles UBP network.

Control System Outputs
The EATC system has 3 control system outputs.

Blower Motor Speed Control
The blower motor speed control controls the blower motor speed by converting low power signals from the EATC 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.

The blower motor speed control is located on the heater core and evaporator core housing near the blower motor.

Temperature Blend Door Actuator
An electric temperature blend door actuator is used to position the temperature blend door. The temperature blend door actuator contains a reversible electric motor to position the temperature blend door. A potentiometer is installed in the actuator to allow the EATC module to monitor the position of the temperature blend 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 return circuit is connected to a wiper which is driven along the variable resistor by the actuator shaft. The signal returned to the EATC module from the wiper indicates the position of the temperature blend door.

Mode Door Actuators
Electric mode door actuators are used to position the 3 airflow mode doors. The 3 mode door actuators each contain a reversible electric motor to position the airflow mode door. A potentiometer is installed in the floor/defrost door and panel door actuators to allow the EATC 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 return circuit is connected to a wiper which is driven along the variable resistor by the actuator shaft. The signal returned to the EATC module from the wiper indicates the position of the airflow mode door. The air inlet mode door actuator is driven to the full RECIRC or full FRESH air inlet position, and does not require a potentiometer circuit to monitor it's position.