Control Components
Control Components
Dual-Zone Electronic Automatic Temperature Control (EATC)
The HVAC 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
- Solar amplifier (sunload sensor)
- Vehicle speed sensor
- Cylinder Head Temperature (CHT) sensor
Using these inputs, the HVAC module determines the correct conditions for the following outputs:
- A/C clutch engagement
- Blower speed
- Temperature blend door position
- Floor mode door position
- Panel/defrost mode door position
- Air inlet mode door position
Control System Inputs
HVAC Module
The HVAC module:
- is located in the instrument panel.
- has a vacuum fluorescent display for displaying set temperature, ambient temperature, function and DTCs.
- utilizes an On-Board Diagnostic (OBD) feature to supply the technician with DTCs. These DTCs help direct the technician to the inoperative component.
Rear Audio/Climate Control Module
The rear audio/climate control module is equipped on limousine (long wheelbase) vehicles. The rear audio/climate control module converts an input from the rear audio/climate control switch, then signals the Audio Control Module (ACM) via the Audio Corporate Protocol (ACP) bus. The ACM then signals the HVAC module over the J1850 communications network (Standard Corporate Protocol (SCP) bus).
Steering Wheel Audio/Climate Control Switch
The steering wheel audio/climate control switch, located on the right side of the steering wheel, allows the driver to adjust the passenger compartment temperature setting. For removal and installation of the steering wheel audio/climate control switch, refer to Information and Entertainment Systems Service and Repair.
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 HVAC 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 A/C evaporator housing and the in-vehicle temperature sensor.
- The automatic temperature control sensor hose and elbow takes air from the A/C evaporator 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 Amplifier (Sunload Sensor)
The solar amplifier supplies information to the HVAC module indicating sunload. For information on the location and service of the solar amplifier, refer to Exterior Lighting Service and Repair.
Control System Outputs
Blower Motor Speed Control
The A/C blower motor speed control:
- is located on the A/C evaporator housing, in the engine compartment.
- converts low power signals from the dual automatic temperature control module to a high current, variable ground feed for the blower motor.
- varies the blower motor speed and is controlled by the HVAC module software.
- provides a gradual increase or decrease in blower motor speed under all conditions by use of a delay function.
Temperature Blend Door Actuators
The dual-zone Electronic Automatic Temperature Control (EATC) system uses 2 temperature blend door actuators to control 2 separate temperature blend doors. The temperature blend doors independently vary the LH and RH temperature settings. The temperature blend door actuators:
- are located on the heater core housing.
- move the temperature blend doors on command from the HVAC module.
- contain a reversible electric 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.
- receive a 5-volt signal at one end of the potentiometer. The voltage available at the wiper indicates the position of each potentiometer. The expressed value of the actuator wiper voltage is sent to the HVAC module and is matched with an expected wiper voltage value. The control module then drives the actuator motor in the direction necessary to make the actuator wiper voltage match with the expected HVAC module setting.
Mode Door Actuators
Two electronic mode door actuators are used to position the airflow mode doors. The mode door actuators:
- are located on the plenum chamber.
- each contains a reversible electric 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.
- each receive a 5-volt signal at one end of the potentiometer. The voltage available at the wiper indicates the position of each potentiometer. The expressed value of the actuator wiper voltage is sent to the HVAC module and is matched with an expected wiper voltage value. The control module then drives the actuator motor in the direction necessary to make the actuator wiper voltage match with the expected HVAC module setting.