Control Components

CONTROL COMPONENTS

MANUAL CLIMATE CONTROL
The manual climate control system heats or cools the vehicle interior depending on the function selector position and the temperature selected. The function selector position determines heating or cooling and air distribution. The temperature blend control setting determines air temperature.

The manual climate control components are used to:
- select the air inlet source (outside or recirculated).
- select the blower motor speed.
- select the discharge air temperature (temperature blend).
- select the discharge air location (defrost, panel, floor).
- select the A/C compressor clutch operation.

Manual Climate Control System Inputs

Climate Control Assembly
The climate control assembly has three system controls:
- The function selector switch combines a vacuum selector valve with two electrical switches to supply battery positive voltage (B+) to the blower motor control circuit and the A/C clutch circuit (if equipped).
- The temperature selection is accomplished with a potentiometer connected to the electric blend door actuator that controls positioning of the temperature blend door. Movement of the control knob from COOL (blue) to WARM (red) causes a corresponding movement on the air temperature control door and determines the temperature that the system will maintain.
- The blower motor switch controls blower motor speed by adding or bypassing resistors in the blower motor resistor.

Manual Climate Control System Outputs

Blower Motor Switch Resistor
The blower motor resistor has the following features:
- It is located on the evaporator core housing in the engine compartment.
- Three resistance elements are mounted on the resistor board to provide four A/C blower motor speeds.
- Depending on the heater blower motor switch position, series resistance is added or bypassed in the A/C blower motor circuit to decrease or increase A/C blower motor speed.
- A thermal limiter will open the resistor coil circuit when the temperature reaches 121°C (250°F), interrupting the blower motor operation in all speeds except HI.
- The thermal limiter cannot be reset and is not repairable.

Temperature Blend Door Actuator
The temperature blend door actuator:
- is located on the top of the plenum chamber behind the glove compartment.
- moves the temperature blend door on command from the temperature control switch.

Vacuum Control Motors
The two vacuum control motors:
- are actuated by vacuum from the function selector switch.
- position the plenum doors to direct system airflow to the vehicle's interior as determined by the function selector switch setting.

ELECTRONIC AUTOMATIC TEMPERATURE CONTROL (EATC)
The EATC system heats or cools the vehicle interior depending on the function and temperature selected. The function selection determines heating or cooling and air distribution. The temperature blend control setting determines air temperature.

The EATC components are used to:
- automatically determine the climate control settings based on the temperature selected and ambient conditions (AUTO mode).
- select the air inlet source (outside or recirculated).
- select the blower motor speed.
- select the discharge air temperature (temperature blend).
- select the discharge air location (defrost, panel, floor).
- select the A/C compressor clutch operation.

EATC System Inputs
The EATC system has five control system inputs.

EATC Module (Climate Control Assembly)
The EATC Module:
- is located in the instrument panel.
- has a vacuum fluorescent display for displaying set temperature, function and diagnostic trouble codes (DTCs).
- utilizes an on-board diagnostic (OBD) feature to supply the technician with diagnostic trouble codes (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.
- 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:
- is attached to left side of the grille opening panel to the left of the A/C condenser core.
- contains a thermistor which measures the temperature of outside air as a resistance and sends that reading to the EATC module.

In-Vehicle Temperature Sensor
The in-vehicle temperature sensor:
- is located in the instrument panel to the right of the steering column.
- contains a thermistor which measures the in-vehicle air temperature and sends that reading to the EATC module.
- utilizes a venturi system with an aspirator hose running between the in-vehicle temperature sensor and the plenum chamber.
- airflow through the plenum chamber creates a suction through the aspirator hose which draws air from the passenger compartment through the in-vehicle temperature sensor.

Solar Amplifier (Sunload Sensor)
The solar amplifier supplies the EATC module with information indicating sunload. For information on the location and service of the solar amplifier, refer to Lighting and Horns.

EATC System Outputs
The EATC system has five control system outputs.

Automatic Temperature Control (ATC) Solenoid and Manifold
The ATC solenoid and Manifold:
- is located in the instrument panel behind the audio unit.
- uses solenoid-type valves to distribute vacuum to the vacuum control motors and the heater control valve based on the EATC module settings.

Blower Motor Speed Control
The blower motor speed control:
- is located on the evaporator core housing behind the suction accumulator.
- varies the blower motor speed and is controlled by the EATC module.
- uses low power signals from the EATC module to control a high-current, variable ground feed to the blower motor.
- 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 Actuator
The temperature blend door actuator:
- is located on the top of the plenum chamber behind the glove compartment.
- moves the temperature blend door on command from the EATC module.
- contains a reversible motor and 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.
- applies a 5-volt signal to the ends of the potentiometer. The expressed value of the actuator wiper voltage is sent to the EATC module and is matched with an expected wiper voltage value. The EATC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected EATC module wiper voltage value.

Vacuum Control Motors
The two vacuum control motors:
- are actuated by the ATC solenoid and manifold based on inputs from the EATC module.
- position the plenum doors to direct system airflow to the vehicles interior as determined by the EATC module settings.