Control Components

CONTROL COMPONENTS

Manual Climate Control
The manual climate 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.

Control System Inputs
The climate control assembly has 3 system control inputs.

Climate Control Assembly
The climate control assembly integrates the temperature control switch, A/C request button and rear defog switch into a single unit.

The temperature control switch setting determines air temperature. Temperature selection is accomplished with a potentiometer (temperature control switch) connected to the temperature blend door actuator. Movement of the temperature control switch 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 manual climate control assembly and a new one cannot be separately installed.

The A/C request switch determines A/C compressor operation, except when the function selector switch is in the OFF, MAX, DEFROST or FLOOR/DEFROST positions. The A/C request switch is an integral part of the manual climate control assembly and a new one cannot be separately installed.

The rear defog button signals activation of the heated backlight and heated mirrors. The rear defog button is an integral part of the manual climate control assembly and a new one cannot be separately installed.

Function Selector Switch
The function selector switch combines a vacuum selector valve that determines air distribution and an electrical switch to supply battery voltage to the A/C compressor circuit and the blower motor circuit. When the function selector switch is in the MAX A/C, DEFROST or FLOOR/DEFROST positions, the A/C compressor will be operational regardless of the A/C request switch status.

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

Control System Outputs
The climate control system has 5 system outputs.

Blower Motor Resistor
The blower motor resistor 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. The blower motor resistor has an overheating device (thermal limiter) that opens the resistor coil when the temperature reaches approximately 184°C (363°F), interrupting the blower motor operation in all speeds except HIGH. The thermal limiter cannot be reset and is not serviceable.

Temperature Blend Door Actuator
The temperature blend door actuator moves the temperature blend door on command from the temperature control switch using a reversible electric motor. The temperature blend door actuator contains an internal controller that will recognize the temperature control switch signal and drive the temperature blend door to the desired position.

The temperature blend door actuator is located on the LH side of the heater core and evaporator core housing.

Vacuum Control Motors
The 4 vacuum control motors move the airflow mode doors to direct system airflow to the vehicle interior as determined by the function selector switch. Vacuum control motors are used to control the:
- air inlet door.
- defrost mode door.
- panel mode door.
- floor mode door.

Heater Control Valve Vacuum Switch
The heater control valve vacuum switch applies vacuum to the heater control valve when the temperature blend door is in the full COOL position. The temperature blend door actuates the heater control valve vacuum switch with an arm attached to the RH side of the temperature blend door pivot shaft.

The heater control valve vacuum switch is mounted on the RH side of the heater core and evaporator core housing just below the defrost door vacuum control motor.

Dual-Zone Electronic Automatic Temperature Control (EATC)
The HVAC 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 HVAC module determines the correct conditions for the following outputs:
- A/C compressor operation
- Blower speed
- LH side temperature blend door position
- RH side temperature blend door position
- Air inlet mode door position
- Defrost mode door position
- Panel mode door position
- Floor mode door position

Control System Inputs
The dual-zone EATC system has 5 control system inputs.

HVAC Module

NOTE: If installing a new HVAC module, the new module must be configured for the vehicle. Refer to Information Bus (Module Communications Network).

The HVAC module has a vacuum fluorescent display for displaying set temperature, airflow direction, blower speed and DTCs. The HVAC module utilizes an on-board diagnostic (OBD) feature to supply the technician with DTCs. These DTCs help direct the technician to the inoperative component.

Steering Wheel Audio/Climate Control Switch
The steering wheel audio/climate control switch is located on the right side of the steering wheel. 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.

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 LH side of the radiator support.

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 Heating and Air Conditioning.

In-Vehicle Temperature Sensor
The in-vehicle temperature sensor contains a thermistor which measures the in-vehicle air temperature and sends that reading to the HVAC module. A hose and elbow is connected between the heater core and evaporator core housing and the in-vehicle temperature sensor. The automatic temperature control sensor hose and elbow takes air from the heater core and evaporator core housing air stream to create a 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 LH side and RH side sunload.

Control System Outputs
The dual-zone EATC system has 4 control system outputs.

Automatic Temperature Control (ATC) Solenoid and Manifold
The automatic temperature control (ATC) solenoid and manifold uses 5 internal solenoid-type valves to distribute vacuum to the vacuum control motors and heater control valve based on the HVAC module settings. Manifold vacuum is always available at the ATC solenoid and manifold from the vacuum reservoir when the engine is running. The 4 vacuum control motors and the heater control valve vacuum lines are each connected to a separate internal solenoid. The HVAC module will apply voltage to the desired solenoids to open the solenoid to the manifold vacuum supply and complete the vacuum circuit to the desired component.

Blower Motor Speed Control
The blower speed control converts 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 Actuators
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 HVAC module applies a 5-volt signal to one end of the potentiometer and ground to the other. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft. The voltage available at the wiper indicates the position of the temperature blend door. The actuator wiper voltage is sent to the HVAC module which drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected HVAC module wiper voltage value.

Vacuum Control Motors
The 4 vacuum control motors move the airflow mode doors to direct system airflow to the vehicle interior as determined by the function selector switch. Vacuum control motors are used to control the:
- air inlet door.
- defrost mode door.
- panel mode door.
- floor mode door.