Control Components

CONTROL COMPONENTS - MANUAL CLIMATE CONTROL

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

The manual climate control system 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 clutch operation.

Control System Inputs
The climate control assembly has 4 system controls:

Function Selector Switch
The function selector switch is separately serviceable from the integrated control panel (ICP), and combines a vacuum selector valve with 2 electrical switches to supply battery voltage (B+) to the A/C clutch circuit and the blower motor speed control circuit.

Temperature Control Switch
The temperature control switch is separately serviceable from the ICP. Temperature selection is accomplished with a potentiometer connected to the electric blend door. Movement of the temperature control switch from COOL (blue) to WARM (red) causes a corresponding movement of the temperature blend door.

Blower Motor Switch
The blower motor switch is separately serviceable from the ICP, and controls blower motor speed by adding or by passing resistors in the heater blower motor switch resistor.

Control System Outputs

Blower Motor Resistor
The blower motor resistor has the following features:
- The assembly is located in the passenger compartment on the heater core and evaporator core housing next to the blower motor assembly.
- Three resistor elements are 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.
- An overheating device (thermal limiter) will open the resistor coil when the temperature reaches 121°C (250°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 is located on the rear of the heater core and evaporator core housing.
- Its function is to move the air temperature blend doors on command from the temperature control switch.

Vacuum Control Motors
The vacuum control motors:
- are located on the A/C evaporator housing, air inlet duct and plenum chamber.
- direct system airflow to the vehicle interior as determined by the function selector switch.

CONTROL COMPONENTS - ELECTRONIC AUTOMATIC TEMPERATURE CONTROL (EATC)
With the use of a microcontroller, the remote climate control module analyzes input from the following major sources:
- Integrated control panel (temperature, air distribution and blower selection)
- In-vehicle temperature
- Ambient temperature
- Sunload
- Vehicle speed
- Engine coolant temperature

Using these inputs, the microcontroller determines the correct conditions for the following outputs:
- A/C compressor operation
- Blower speed
- Air temperature blend door position
- Airflow mode door position
- Defroster door position
- Air inlet door position

Control System Inputs

Integrated Control Panel
The integrated control panel (ICP) combines the audio unit and climate controls as an assembly. The ICP has the following climate control features:
- It is used to supply the remote climate control module with function/mode selection information.
- It contains a blower speed override control for manual input.
- It has a vacuum fluorescent display for displaying set temperature, ambient temperature, function and diagnostic trouble codes (DTCs).

Remote Climate Control (RCC) Module
The remote climate control module is used to control the climate control system based on input from the ICP. The remote climate control module has the following features.
- It is mounted to the heater core and evaporator core housing, to the left of the blower motor.
- It communicates with the ICP using the CAN network.
- Uses an On-Board Diagnostic (OBD) feature to supply the technician with diagnostic trouble codes (DTCs). These DTCs direct the technician to the inoperative component.

A/C Ambient Air Temperature Sensor
The A/C ambient air temperature sensor:
- is located in front of the A/C condenser core near the center of the vehicle.
- contains a thermistor which measures the temperature of outside air as a resistance and sends that reading to the RCC 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 in-vehicle temperature sensor hose and elbow is connected between the A/C evaporator housing and the in-vehicle temperature sensor.
- The in-vehicle temperature sensor hose and elbow takes air from the A/C evaporator housing air stream to create a suction in the in-car temperature sensor.
- The suction draws in-vehicle air into the in-vehicle temperature sensor and across the thermistor.

Solar Amplifier (Sunload Sensor)
For additional information on the location and service of the solar amplifier, refer to Lighting and Horns.

Control System Outputs

Blower Motor Speed Control
The blower motor speed control is located under the heater core and evaporator core housing, near the blower motor.
- The function of the blower motor speed control is to convert low power signals from the RCC module to a high current, variable ground feed for the blower motor.
- Blower motor speed is infinitely variable and is controlled by the RCC module software.
- A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

Temperature Blend Door Actuator
The temperature blend door actuator is located on the rear of the A/C evaporator housing.
- Its function is to move the air temperature blend doors on command from the remote climate control module.
- The temperature blend door actuator 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 air temperature blend door.
- A 5-volt signal is applied to the ends of the potentiometer. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the remote climate control module and is matched with the wiper voltage of the module potentiometer. The remote climate module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the remote climate control module wiper voltage.

Vacuum Control Motors
The vacuum control motors:
- are located on the A/C evaporator housing, air inlet duct and plenum chamber.
- direct system airflow to the vehicle interior as determined by the RCC module or manual override.