Self-diagnosis System

1.Description
In the self-diagnosis system, the ECU transmits any abnormality that occurs in the indicator, sensors, and actuator to the control panel for display to notify the technician. This system is useful for diagnosis because the self-diagnosis results are stored in memory even after the ignition switch is turned off.
Various checks can be performed with the switch operation as shown in the illustration.

Self-diagnosis System

2.Indicator check
Indicators such as switches, temperature setting display and beep activation can be checked. The indicators of the switches and temperature setting display come on four times and go off.
HINT:
In some models, beep for operation check may sound.
3.Sensor check
Past or present failures of the sensors can be checked.
When more than one failure is found, pressing the A/C switch will allow all the failures to be viewed one by one.
When the solar sensor is checked indoors, open circuit may be displayed. Expose the solar sensor to incandescent light (fluorescent light is not effective for the check) indoors, or expose to the sunlight outside to check the solar sensor.
In some models, beep to present failure.
4.Actuator check
A patterned output is transmitted to the actuator to check its performance.
The technician can check for failure of the actuator by transmitting signals from the ECU and activating the airflow dampers, air inlet damper, air mix damper, compressor, etc.
DTC or other data can be checked by connecting the hand-held tester to the DLC3.

1.What is TAO?
In order to speedily adjust the interior temperature to the set temperature, the ECU calculates the outlet air temperature (Temperature Air Outlet, TAO) based on the temperature information transmitted from each sensor.
The calculation of TAO is based on the interior temperature, ambient temperature and amount of sunlight in relation to the set temperature.
Although auto A/C controls the temperature mainly with the interior temperature information, it also utilizes ambient temperature and sunlight amount detection for more precise control.
The outlet air temperature (TAO) is lowered in the following conditions:
Temperature setting is lowered
Interior temperature is high
Ambient temperature is high
Sunlight is strong
Airflow Temperature Control
1.Description
In order to speedily adjust the interior temperature to the set temperature, the airflow temperature controlled by changing the ratio of hot and cold air by adjusting the air mix damper position (opening).
In some models, the water valve opening also changes according to the damper position.
2.Control
(1)MAX control
When the temperature is set at MAX COOL or MAX HOT, the air mix damper is fully to the COOL side or HOT side regardless of the TAO value.
This is called “MAX COOL control” or “MAX HOT control.”
(2)Normal control
When the temperature is set between 18.5-31.5°C (65.3-88.7°F), the air mix damper position is controlled based on the TAO value in order to adjust the interior temperature to the set temperature.
(3)Calculation of air mix damper opening
Supposing the opening of the air mix damper to be 0% when it is moved fully to the COOL side, and 100% when it is moved fully to the HOT side, the evaporator temperature becomes nearly equal to TAO when the opening is 0%. When the opening is 100%, the heater core temperature calculated from the engine coolant temperature becomes equal to TAO.
ECU allows power conduction to the servomotor to control the opening of the air mix damper in order to adjust the actual damper opening detected by the potentiometer to the target opening level.
Target damper opening = (TAO – Evaporator temperature) / (Coolant temperature – Evaporator temperature) X 100

1.Individual A/C control for left and right
In some models, the temperature and airflow control can be performed based on individual temperature setting of driver’s side and front passenger side.
The temperature and airflow control is performed in the following ways:
Control with damper
The air mix damper is fitted for the left and right to allow individual temperature control.
Control with film damper
The step motor retracts the film damper with holes and adjusts the location of the holes to allow individual temperature and airflow control.
Not all vehicles use the duct sensors for individual temperature control for the left and right vents.
In some models airflow is controlled individually for the left and right by airflow control even when the vehicle utilizes damper (plate type).

Airflow Control

1.Description
When the A/C is switched between heater and cooler, the A/C mode is automatically switched for the desired airflow.
2.Control
The airflow control is switched in the following way:
When lowering the interior temperature: FACE
When the interior temperature is stable around the set temperature: BI-LEVEL
When heating the interior: FOOT

Blower Speed Control

1.Description
The air volume is controlled by automatic adjustment of the blower motor speed based on the gap between the interior and set temperatures.
When there is a big difference in temperature:
Hi blower motor speed
When there is a small difference in temperature:
Lo blower motor speed
2.Auto control
The current to the blower motor is controlled by adjusting the base current of the power transistor. Based on the gap between the interior and set temperatures, the blower speed is continuously controlled with TAO value.
3.EX-HI relay control
EX-HI relay directly grounds the motor when the MAX air blow is required.
As this relay avoids voltage loss of the power transistor, the “saved” voltage can be utilized to generate the maximum blower speed.
4.Manual control
The blower speed can be adjusted manually by the blower speed selector setting.
Function of LO resistor:
A large amount of current flows when the blower motor is activated. In order to protect the power transistor, LO resistor receives current first before the power transistor turns on

1.Control
When the airflow mode is set at FOOT or BI-LEVEL and blower speed selector is set at AUTO, the blower speed is controlled based on the coolant temperature.
(1)When the coolant temperature is low
To stop the cool wind, warm-up control restricts the blower fan from turning.
(2)When warming up
Warm-up control compares the air volume detected by the coolant temperature sensor and that calculated from TAO, takes the lower value, and provides lower blower speed.
(3)After warming up
Warm-up control performs normal control based on TAO.
This control is activated only for heating, not for cooling.

Time-lag Airflow Control

1.Description
When a vehicle is parked under the hot sun for a long time, the air conditioner releases hot air immediately after the activation. The time-lag airflow control function prevents such a problem.
2.Control
(1)When the evaporator temperature is above 30°C (86°F)
As shown in the figure, the time-lag control turns off the blower motor and leaves it off for about four seconds with the compressor turned on, cooling the air inside the cooling unit. For about five seconds thereafter, it runs the blower at LO to release the air cooled in the cooling unit to the vehicle interior.
(2)When the evaporator temperature is below 30°C (86°F)
As shown in the figure, the time-lag control runs the blower at LO for about five seconds.

1.Description
Air inlet control normally introduces exterior air. When the gap between the interior temperature and the set temperature is large, the air inlet control automatically switches to the interior air re-circulation mode for more effective cooling.
2.Control
The air inlet control functions in the following way:
Normally: FRESH
When the interior temperature is high: RECIRC
In some vehicles, air inlet control also switches to RECIRC automatically if the level of CO (carbon monoxide), HC (hydrocarbons), and NOx (oxides of nitrogen) in the exterior air detected by the smog ventilation sensor exceeds the specified level.
When the DEF mode is selected for airflow, the air inlet control switches to FRESH mode automatically. (This control is not available in some models.)

Neural Network Control (Reference)
Description
Even at the same TAO, each passenger feels the temperature differently depending on the environment. With the conventional auto A/C system that uses the calculated TAO as the basis for all control, temperature adjustment considering the individual passenger’s feeling was difficult, as such feeling is too complex to be formulated.
In order to provide a high level of control that even senses the passenger’s feeling, neural network technology was adopted. Neural network is the engineering model of the neural information transmission of organism. The neuron model for the complex relations between input and output of neurotransmission of humans is structured.
Neural network is the combination of several neuron models and consists of input, intermediate, and output layers.

1.Air mix servomotor
(1)Construction
The air mix servomotor consists of the motor, limiter, potentiometer and moving contact, etc., as shown in the figure and it is activated by the signal from the ECU.
(2)Operation
When the air mix damper is shifted to HOT, the MH terminal will be the power source and the MC terminal will be the ground to rotate the servomotor to make the shift. When the MC terminal becomes the power source and the MH terminal becomes the ground, the servomotor rotates in the opposite direction to shift the air mix damper to COOL.
The moving contact of the potentiometer moves in synchronicity with the servomotor revolving, generates electric signals according to the damper position, and feeds back the actual damper position to the ECU. When the damper comes to the desired position, the air mix servomotor stops the current to the servomotor.
The air mix servomotor is equipped with a limiter that shuts off the current to the motor when full-stroke movement is activated. When the moving contact that synchronizes with the servomotor revolving reaches the full-stroke positions, the circuit is open to stop the motor.
2.Air inlet servomotor
(1)Construction
The air inlet servomotor consists of the motor, gear, moving plate, etc., as shown in the figure.
(2)Operation
Pressing the air inlet control switch will generate the ground circuit for the servomotor to allow the current to the motor and moves the air inlet damper.
When the damper is changed to FRESH or RECIRC position, the contact of the moving plate linked with the motor is released and the circuit is open to stop the motor.
3.Airflow servomotor
(1)Construction
The airflow servomotor consists of the motor, moving contact, circuit plate, motor drive circuit, etc., as shown in the figure.
(2)Operation
When the airflow control switch is operated, the motor drive circuit determines whether the damper position changes to the right or left side and directs the flow of current to the motor to shift the moving contact linked to the motor.
When the moving contact moves to the position according to the airflow control switch position, the contact with the circuit plate is released, the circuit is open and the motor stops.
When the airflow control switch is moved from FACE to DEF
Input A will be 1 because the circuit is open, and input B will be 0 because the grounded circuit is generated. As a result, output D will be 1 and output C will be 0 and allow the current for the motor from D to C. After the motor revolves and moving contact B releases contact with DEF, input B will be 1 because the circuit will be opened. As a result, both output C and D will be 0, the current to the motor is cut and the motor stops.
Some models do not have a contact in the servomotor.
A/C control ECU rotates the motor based on the operation of the selector on the control panel.
Damper position is monitored in reference to the potentiometer voltage that varies according to the motor.

1.Interior temperature sensor
(1)Construction
The interior temperature sensor uses the thermistor and is installed in the instrument panel with the aspirator. The aspirator utilizes the air blown from the blower to suck the air inside the vehicle in order to detect the average interior temperature.
(2)Function
It detects the interior temperature that is used as the basis for the temperature control.
2.Ambient temperature sensor
(1)Construction
The ambient temperature sensor uses the thermistor and is installed at the front of the condenser. It detects the exterior temperature.
(2)Function
It detects the exterior temperature that is used for controlling the fluctuation of the interior temperature caused by the exterior temperature fluctuation.
3.Solar sensor
(1)Construction
The solar sensor uses a photodiode and is installed in the upper portion of the instrument panel. It detects the amount of sunlight.
(2)Function
It detects the amount of sunlight that is used for controlling the fluctuation of the interior temperature caused by the amount of sunlight fluctuation.
4.Evaporator temperature sensor
(1)Construction
The evaporator temperature sensor uses the thermistor and is installed on the evaporator. It detects the temperature of the air passing through the evaporator (surface temperature of the evaporator).
(2)Function
It is used for frost prevention, temperature and time-lag airflow control.
5.Water temperature sensor
(1)Construction
The water temperature sensor uses the thermistor. It detects the coolant temperature based on the engine water temperature sensor. The signal is transmitted from the engine ECU.
In some models, the water temperature sensor is installed at the heater core.
(2)Function
It is used for temperature control, warm-up control, etc.
Some vehicles are equipped with the following sensors.
Duct sensors
The duct sensors use the thermistor and are installed at inside of the side register. It detects the temperature of the air blown toward the side register and precisely controls the air temperature of the individual airflow.
Smog ventilation sensor
The smog ventilation sensor is installed in the front portion of the vehicle and detects the level of CO (carbon monoxide), HC (hydrocarbons), and NOx (oxides of nitrogen) to control switching between FRESH and RECIRC.

Outline

1.    Auto A/C (Air Conditioner) System
The auto A/C system is activated by setting the desired temperature with the temperature selector and pressing the AUTO switch. The system immediately adjusts and maintains the temperature at the set level with the automatic control of the ECU.

Location
The auto A/C is controlled by the following components:
1.A/C control ECU (or A/C amplifier)
2.Engine ECU
3.Control panel
4.Interior temperature sensor
5.Ambient temperature sensor
6.Solar sensor
7.Evaporator temperature sensor
8.Water temperature sensor (engine ECU sends the signal)
9.A/C pressure switch
10.Air mix servomotor
11.Air inlet servomotor
12.Airflow servomotor
13.Blower motor
14.Blower controller (controls blower motor)
In some models, the following components are also used for the auto A/C control.
Duct sensors
Smog ventilation sensor

ECU

1.A/C control ECU
The ECU computes the temperature and volume of the air to be blown and determines which vents to use based on the temperature detected by each sensor and the set temperature.
These values are used to control the air mix damper position, blower motor speed, and airflow damper positions.
In some models, MPX (multiplex communication system) is used to transmit operation signals from the control panel to the A/C control ECU.

When the automatic light control sensor detects level of the ambient light while the light control switch is in the AUTO position (or in the OFF position for the models without the AUTO position), it transmits a signal to the light control unit, which turns on the taillights and then the headlights depending on the ambient brightness.
The system also has a function that turns on the taillights but prevents the headlights from turning on briefly in cases where it becomes dark for a moment, such as when driving under a bridge or down a tree-lined street when ambient are bright. However, if after a certain lag time has elapsed, the ambient brightness is lower than a specified value, the headlights will come on.
There are various types depending on the model, such as a type in which the automatic light control sensor and light control unit are one unit or a type in which the taillights and headlights come on at the same time.

When the automatic light control sensor detects level to the ambient light, it outputs a pulse signal to terminal A of the light control unit. When the light control unit judges the decrease in ambient brightness, and activates the taillight and headlight relays to turn on the taillight and headlight.
When the light control unit judges an increase in ambient brightness, the taillights and headlights go off.

When the automatic light control sensor detects level of the ambient light while the light control switch is in the AUTO position (or in the OFF position for the models without the AUTO position), it transmits a signal to the light control unit, which turns on the taillights and then the headlights depending on the ambient brightness.

The system also has a function that turns on the taillights but prevents the headlights from turning on briefly in cases where it becomes dark for a moment, such as when driving under a bridge or down a tree-lined street when ambient are bright. However, if after a certain lag time has elapsed, the ambient brightness is lower than a specified value, the headlights will come on.

There are various types depending on the model, such as a type in which the automatic light control sensor and light control unit are one unit or a type in which the taillights and headlights come on at the same time.

When the automatic light control sensor detects level to the ambient light, it outputs a pulse signal to terminal A of the light control unit. When the light control unit judges the decrease in ambient brightness, and activates the taillight and headlight relays to turn on the taillight and headlight.
When the light control unit judges an increase in ambient brightness, the taillights and headlights go off.