Electronic Manual Temperature Control
The electronic manual temperature control (EMTC) 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 EMTC system has two system control inputs.
Blower Motor Switch
The blower motor switch is mounted in the climate control assembly and controls blower motor speed by adding or bypassing resistors in the blower motor resistor in all modes except OFF.
Control System Outputs
The EMTC system has three 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 four 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 will open the resistor when the temperature reaches approximately 220°C (428°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(s)
The temperature blend door actuator(s)
- is located on the heater core and evaporator core housing.
- moves the temperature blend door(s) on command from the EMTC 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.
- applies a 5-volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the EMTC module and is matched with an expected wiper voltage value. The EMTC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected EMTC module wiper voltage value.
- Vehicles with single-zone EMTC use a single temperature blend door actuator. Vehicles with dual-zone EMTC use one temperature blend door actuator for the LH side of the vehicle, and one temperature blend door actuator for the RH side of the vehicle.
Mode Door Actuators
The 2 mode door actuators
- include the air inlet door and defrost/panel/floor mode door actuators.
- direct system airflow to the vehicle interior as determined by the climate control assembly.
- each contain a reversible electric motor.
- (defrost/panel/floor mode door actuator only) contains a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the mode door.
- (defrost/panel/floor mode door actuator only) apply a 5-volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the EMTC module and is matched with an expected wiper voltage value. The EMTC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected EMTC module wiper voltage value.
Electronic Automatic Temperature Control
The electronic automatic temperature control (EATC) module analyzes input from the following major sources
- temperature, airflow direction, blower, A/C and RECIRC selection (made by the vehicle occupants)
- in-vehicle temperature sensor
- ambient temperature sensor
- solar radiation sensor
- vehicle speed
- engine coolant temperature
Using these inputs, the EATC module determines the correct conditions for the following outputs
- A/C compressor operation
- blower speed
- temperature blend door position
- defrost/panel/floor door position
- air inlet door position
The EATC system has 4 control system inputs.
EATC Module
The 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.
- display will switch between Celsius and Fahrenheit when the instrument cluster display is toggled.
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 aspirator hose and elbow is connected between the heater core and evaporator core housing and the in-vehicle temperature sensor.
- The aspirator 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 EATC module indicating sunload.
Ambient Temperature Sensor
The ambient temperature sensor signal is received by the smart junction box (SJB) which communicates it to the EATC module via the SCP network.
The EATC system has three control system outputs.
Blower Motor Speed Control
The blower speed control
- is located on the heater core and evaporator core housing near the blower motor.
- PWM signals from the EATC module to control a high-current, variable ground feed for the blower motor.
- varies the blower motor speed and is controlled by the EATC module software.
- has a delay function to provide a gradual increase or decrease in blower motor speed under all conditions.
The temperature blend door actuator(s)
- are located on the heater core and evaporator core housing.
- moves the temperature blend door(s) on command from the 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(s).
- applies a 5-volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position 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.
- Vehicles with single-zone EATC use a single temperature blend door actuator. Vehicles with dual-zone EATC use one temperature blend door actuator for the LH side of the vehicle, and one temperature blend door actuator for the RH side of the vehicle.
The 2 mode door actuators
- include the air inlet door and defrost/panel/floor mode door actuators.
- position the plenum doors to direct system airflow to the vehicle interior as determined by the EATC module settings.
- contains a reversible electric motor.
- (defrost/panel/floor mode door actuator only) contains a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the mode door.
- (defrost/panel/floor mode door actuator only) apply a 5-volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position 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.
Refer to CLIMATE CONTROL SYSTEM-GENERAL INFORMATION .
