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.

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.

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.

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 4 system outputs.

Blower Motor Resistor
The blower motor resistor:
- is located on the heater core and evaporator core housing near the blower motor.
- has three 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.
- 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.
- is serviced as an assembly. The thermal limiter cannot be reset and is not serviceable.

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 of the temperature control switch.
- contains a reversible electric motor.

Vacuum Control Motors
The 4 vacuum control motors:
- direct system airflow to the vehicle interior as determined by the function selector switch.

Heater Control Valve Vacuum Switch
The heater control valve vacuum switch controls operation of the heater control valve. 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.
- is actuated by an arm attached to the temperature blend door RH pivot shaft.
- applies vacuum to the heater control valve when the temperature blend door is in the full COOL position.

DUAL AUTOMATIC TEMPERATURE CONTROL
The dual-zone 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 dual-zone EATC 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
- Panel airflow door position
- Floor airflow door position
- Defrost airflow door position
- Air inlet door position

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

Dual-Zone EATC
The dual-zone EATC module:
- is located in the instrument panel.
- has a vacuum fluorescent display for displaying set temperature, airflow direction, blower speed and diagnostic trouble codes (DTCs).
- utilizes an on-board diagnostic (OBD) feature to supply the technician with diagnostic trouble codes (DTCs). These DTCs 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.
- allows the driver to adjust the passenger compartment temperature setting and manually override the blower motor speed setting.

Ambient Air Temperature Sensor
The ambient air temperature sensor and bracket:
- is located in front of the condenser core.
- contains a thermistor which measures the temperature of outside air as a resistance and sends that reading to the dual-zone EATC module.

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 automatic temperature control sensor 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
The solar radiation sensor supplies information to the dual-zone EATC 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 ATC solenoid and manifold:
- is located on the heater core and evaporator core housing near the blower motor.
- uses solenoid-type valves to distribute vacuum to the vacuum control motors and heater control valve based on the settings of the dual-zone EATC module.

Blower Motor Speed Control
The blower speed control:
- is located on the heater core and evaporator core housing near the blower motor.
- converts low power signals from the dual-zone EATC module to a high current, variable ground feed for the blower motor.
- varies the blower motor speed and is controlled by the dual-zone EATC module software.
- has a delay function to provide a gradual increase or decrease in blower motor speed under all conditions.
- controls the integral high blower speed relay which is engaged when maximum fan speed is selected.

Temperature Blend Door Actuators
The dual-zone EATC system utilizes 2 temperature blend door actuators to control 2 separate temperature blend doors that independently vary the LH side and RH side temperature settings, as desired. The temperature blend door actuators:
- are located on the heater core and evaporator core housing.
- moves the temperature blend door on command from the dual-zone EATC 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.
- apply a 5-volt signal to one end of the potentiometers and ground to the other. The voltage available at the wiper indicates the position of each potentiometer. The expressed value of the actuator wiper voltage is sent to the dual-zone EATC module and is matched with an expected wiper voltage value. The dual-zone EATC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected dual-zone EATC module wiper voltage value.

Vacuum Control Motors
The 4 vacuum control motors:
- are actuated by the ATC solenoid and manifold based on input from the dual-zone EATC module.
- position the airflow mode doors to direct system airflow to the vehicle interior as determined by the dual-zone EATC module settings.