Control Components

DUAL ELECTRONIC AUTOMATIC TEMPERATURE CONTROL
With the use of a microcontroller, the Dual Automatic Temperature Control (DATC) module analyzes input from the following major sources:
- temperature, function and blower selection (made by the vehicle occupants)
- in-vehicle temperature sensor
- ambient temperature sensor
- dual sunload sensor
- vehicle speed
- engine rpm
- engine coolant temperature
- actuator door position controls
- driver and passenger heater core air discharge temperature sensors
- evaporator discharge temperature

Using these inputs, the microcontroller determines the correct conditions for the following outputs:
- A/C clutch engagement
- blower speed
- cold air bypass door position
- panel door position
- defrost door position
- floor door position
- air inlet duct door position
- driver coolant control valve
- passenger driver coolant control valve
- electric water pump
- heater wiper rest or heated windshield
- heated rear window rear defog
- external temperature (outside temperature display)


Control System Inputs

Climate Control Assembly
The Dual Automatic Temperature Control (DATC) module, located in the instrument panel, has the following features:
- a blower speed override control for manual input
- individual temperature set controls for driver and passenger
- an A/C request control for manual input
- a recirculated air control for manual input
- a vacuum fluorescent display for displaying set temperatures for both the driver and passenger, external or ambient temperature, blower speed setting and Diagnostic Trouble Codes (DTCs)
- an On-board Diagnostic (OBD) feature to supply the technician with Diagnostic Trouble Codes (DTCs). These DTCs direct the technician to the inoperative component.
- air distribution mode overrides
- rear defog control
- heated wiper rest or heated windshield
- EXT temperature control to display external or outside temperature
- F/C control to toggle between English or metric settings.

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 dual automatic temperature control assembly.

In-Vehicle Temperature Sensor
The in-vehicle temperature sensor is located in the instrument cluster finish panel. The 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 is connected between the A/C plenum housing and the in-vehicle temperature sensor.
- The automatic temperature control sensor hose and venturi takes air from the A/C plenum housing to create a suction across the in-vehicle temperature sensor.
- The suction draws in-vehicle air into the in-vehicle temperature sensor and across the thermistor.

Dual A/C Sunload Sensor
The dual A/C sunload sensor:
- is located on the top center of the instrument panel in the defroster grille.
- contains photovoltaic diodes that are sensitive to sunlight.
- generates small amounts of current across the terminals depending upon the amount of light reaching the photovoltaic diode; therefore the only test that can be carried out is for an internal short circuit, an open circuit or sensor value out-of-range.
- contains an internal diagnostic resistor to allow the DATC module to detect a difference between an open circuit and no sunlight.

Control System Outputs

A/C Blower Motor Speed Control
The A/C blower motor speed control is located on the A/C evaporator housing.
- The function of the A/C blower motor speed control is to convert low power signals from the dual electronic automatic temperature control module to a high current, variable ground feed for the blower motor.
- Blower motor speed is infinitely variable and is controlled by the dual electronic automatic temperature control module software.
- A delay function provides a gradual increase or decrease in blower motor speed under all conditions.
- Controls the integral high blower relay which is engaged when maximum fan speed is selected.

A/C Electronic Air Inlet Door Actuator
The A/C electronic air inlet door actuator is located on the evaporator housing. The air inlet door position determines whether outside or recirculated air is being used.
- The actuator positions the air inlet door on command from the control assembly.
- The air inlet door actuator contains a reversible electric motor and a potentiometer.
- A 5 volt signal and ground reference is applied to the ends of the potentiometer. The voltage available at the wiper indicates the position of the potentiometer. The target position of the actuator is calculated by the DATC module and is matched with the wiper voltage of the actuator. The control module will drive the actuator motor in the direction necessary to make the actuator wiper voltage agree with the control module target position.

Cold Air Bypass Door Actuator
The cold air bypass door actuator is located on the evaporator core housing. During automatic operation the control module can position the door fully open so that some of the airflow will not pass through the heater core. This will provide for maximum cooling. The door is closed or partially closed during modes other than maximum cooling.
- The cold air bypass door actuator positions the cold air bypass door on command from the DATC module.
- Operation of the cold air bypass door actuator is the same as the air inlet door.

Defrost Door Actuator
The defrost door actuator is located on the plenum chamber. The actuator will position the defrost door fully open during defrost operation, partially open during floor/defrost and floor mode operation and fully closed during all other operations.
- The defrost door actuator positions the defrost door on command from the DATC module.
- Operation of the defrost door actuator is the same as the air inlet door.

Panel, Floor Console Door Actuator
The panel, floor console door actuator is located on the plenum chamber. The actuator operates the panel door which is mechanically linked to the floor console door. The actuator positions the panel door and floor console door fully open during panel mode and partially open during floor/panel operation. The doors are closed during other operations.
- The panel, floor console door actuator positions the panel and floor console doors on command from the DATC module.
- Operation of the panel door actuator is the same as the air inlet door.

Floor Outlet Door Actuator
The floor outlet door actuator positions the floor outlet door fully open during floor and floor/panel and floor/defrost operations. The door is closed during other operations.
- The floor outlet door actuator positions the floor outlet door on command from the DATC module.
- Operation of the floor door actuator is the same as the air inlet door.
- The floor outlet door actuator is in the full open position in OFF mode.