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.Function
In idle state such as in slow traffic or during stop, the engine output is small.
In this state, driving the compressor applies overload to the engine, which results in overheating or engine stalling. So, an idle-up device is installed to make the idle speed a little higher to use the A/C.
2.Operation
An engine ECU that receives an A/C switch-on signal opens the idle speed control valve a little to increase intake air to make the engine revolve at the appropriate speed.

Electric Fan Control

1.Function
An electric fan cools the condenser when the A/C is in operation to increase the cooling capability.
2.Operation
In the vehicle that cools the radiator by electric fan, combining two fans for radiator and for condenser controls the cooling capability in three levels (stop, low speed, high speed). When the A/C is in operation, the connection of the two electric fans switches to series connection (low speed) or to parallel connection (high speed) depending on the condition of the refrigerant pressure and the coolant temperature.
When refrigerant pressure is high or engine coolant temperature is high, two electric fans are connected in parallel and rotate at a high speed.
When refrigerant pressure is low or engine coolant temperature is low, two electric fans are connected in series and rotate at a low speed.
Recent models have not only the type that switches fan connection by relay (series connection, parallel connection) but also the type that adjusts the current flow into the electric fan by engine ECU and cooling fan ECU.
The connecting method between the relay and fan and ON/OFF operation of the relay vary depending on the model.

1.Function
The dual A/C and the refrigeration cycle with rear cooler have evaporators and expansion valves for front and rear. These make the refrigerant circulate using a compressor.
To control two refrigerant circuits, solenoid valves are set up.
2.Operation
When the front A/C switch is turned on, current passes through the front solenoid valve and it turns on (opens), while current does not pass through the rear solenoid valve, so the valve turns off (closes). Therefore, the refrigerant flows only in the front side circuit.
When the rear A/C switch is turned on, current passes through both the front side and the rear side and both of the valves turn on (open), so refrigerant passes into the refrigerant circuits on the front side and rear side.
In some models, current passes through only the rear solenoid valve when only the rear A/C switch is turned on.

1.Function
A pressure switch is installed on the high-pressure side of the refrigeration cycle. When the switch detects abnormal pressure in the refrigeration cycle, it stops the compressor to prevent the trouble from expanding to protect the components in the refrigeration cycle.
2.Abnormal low pressure detection
Working the compressor when the refrigerant in the refrigeration cycle is extremely insufficient or when no refrigerant is in the refrigeration cycle due to a gas leak or other causes deteriorates the lubrication of the compressor oil, which could cause the compressor to seize. When the refrigerant pressure abnormally lowers (less than 0.2 MPa (2kgf /cm²)), turning the pressure switch off turns the magnetic clutch off.
3.Abnormal high pressure detection
The refrigerant pressure in the refrigeration cycle might become abnormally high when the condenser is cooled insufficiently or when the refrigerant charge amount is excessive. This condition could break the components of the refrigeration cycle.
When the refrigerant pressure is abnormally high (more than 3.1 MPa (31.7 kgf/cm²)) turning the pressure switch off turns the magnetic clutch off.

Evaporator Temperature Control

1.Function
To prevent the evaporator from frosting, the surface temperature of the evaporator controls the compressor operation.

The surface temperature of the evaporator is detected by thermistor and when the temperature is below a certain degree, the magnetic clutch is turned off to prevent the evaporator from dropping below 0°C (32°F). The air conditioner with EPR doesn’t require this control.

Drive Belt Protection System

1.Function
When the vane pump of the power steering, alternator and other devices are driven together with the compressor by the drive belt, if the compressor locks and the belt is cut, the other devices also do not work. This is a system to prevent the drive belt from being cut by turning the magnetic clutch off when the compressor locks. At the same time, the system causes the A/C switch indicator light to blink to inform the driver of the malfunction.
2.Construction
Every time the compressor turns, signals are produced at the coil in the speed sensor. The ECU detects the compressor revolution by counting the speed of the signals.
3.Operation
It compares the speed of the engine to that of the compressor. If the difference exceeds a certain value, the ECU judges that the compressor locks, and turns the magnetic clutch off. In addition, the ECU causes the A/C switch lamp to blink to inform the driver of the malfunction.

Compressor Two-stage Control System

1.Function
This system changes the timing to turn the compressor off depending on the evaporator temperature and controls the operational ratio. If the operational ratio of the compressor is lower, the fuel economy and the drive feeling are improved.
2.Operation
When the A/C switch is on, this controls so that the compressor is turned off when the detected temperature of the thermistor is below approximately 3°C (37.4°F), and turned on when it is 4°C (39.2°F) or higher. This is cooling performed in the range in which the evaporator does not frost.
When the ECON switch is on, this controls so that the compressor is turned off when the detecting temperature of the thermistor is below approximately 10°C (50°F), and turned on when it is 11°C (51.8°F) or higher. For this reason, the cooling becomes weak, but the operational ratio of the compressor decreases.
To change the operational ratio, some systems use a wobble plate type compressor to vary continuously.

Outline

1.Description
To operate the A/C normally or to reduce the damage to the components when a malfunction occurs, the signals from each sensor or switch are sent to the A/C amplifier in order to control the A/C.
(1)Pressure switch control:
This detects the abnormal rise of refrigerant pressure and turns off the magnetic clutch to protect the components in the refrigeration cycle and stops the compressor from operating.
(2)Evaporator temperature control:
This detects the surface temperature of the evaporator, and turns the magnetic clutch on and off to control the operation of the compressor so that the evaporator does not frost.
(3)Drive belt protection system:
This detects the lock of the compressor, prevents the drive belt from being damaged by turning off the magnetic clutch, and causes the A/C switch indicator light to blink.
(4)Compressor two-stage control system:
This controls the utilization rate of the compressor and improves fuel economy and driveability.
(5)Dual A/C (rear cooler) control:
This turns the magnetic valve on and off to control the dual refrigerant circuits.
(6)Idle-up control:
This stabilizes the engine idling when the A/C is on.
(7)Electric fan control:
This controls the electric fan and improves the cooling capability and fuel economy and reduces noise.

1.Blower speed control function
Adjusting the amount of the current that passes the blower motor controls the blower speed. There are 2 methods:
resistor and transistor.
(1)Resistor type
This adjusts the amount of current using blower resistor. The construction is that 2 resistors are connected in a series. By operating the selector, the resistance value in the circuit is changed, which varies the amount of current to flow.
When placing the selector in the “LO” position, current passes all the resistors. Therefore, current flowing through the motor is reduced and blower speed becomes low. When placing the selector in the “3″ position, current passes only one resistor. When placing the selector in the “HI” position, no current passes any resistors, Therefore, current flowing through the blower motor and blower speed become the highest.
(2)Transistor type
This adjusts the amount of current using a power transistor. Compared to the resistor type, this can control the blower speed at an increased number of levels than the resistor type, so this is mainly used for automatic A/C.

1.Basic theory of cooling
We feel a little cold even on a hot day after swimming. This is because the water on the body takes away the heat when it evaporates from the body.

For the same reason, we feel cool when we apply alcohol to our arms: the alcohol takes away the heat from the arms when it evaporates. We can make objects cooler using these natural phenomena, e.g., by causing a liquid to take the heat from a substance when it evaporates.

A container provided with a tap is placed in a well-insulated box. A liquid that will vaporize readily at atmospheric temperature is placed in the container.

When the tap is opened, the liquid in the container will take away the heat necessary for vaporization from the air inside the box, turn into a gas and escapes outside.

At this time, the temperature of the air inside the box will become lower than that before the tap was opened.

Description of AVC-LAN

1.Outline
AVC-LAN is an acronym for Audio signal, Video signal, and Control signal. It is a unified standard developed by six companies including Toyota Motor Corporation.
Previously, the system could be combined with the products only at the same manufacturer, however, since AVC-LAN has been adopted, each component for AVC-LAN can be selected and the connection can be done at the user’s will owing that the standard is unified.

2.Address of Audio signal, Video signal, and Control signal
AVC-LAN is a rule for the conversation between the microcomputers in each component.
There are many components.
Each component and its function should be numbered to distinguish them. These numbers are called addresses.
(1)Physical address
This address is allocated to each component (radio, CD player, etc.).
(2)Logical address
This address is allocated to each function (tuner function, command switch function, etc.).
3.AVC-LAN control
In AVC-LAN, since various system configurations are possible, each system should identify what the present system configuration is like.
Therefore, registration process is performed to detect the ignition switch ACC position.
The registration process indicates that each component accesses the master component that has the smallest physical address.

Description of Audio signal, Video signal, and Control signal
4.Diagnosis mode
The diagnosis codes of the AVC-LAN include the diagnosis code that indicates individual malfunction in each component and the diagnosis code of AVC-LAN that indicates network communication malfunction. The display of the diagnosis code indicates the malfunction’s physical address or logical address. Based on the information, the system determines the malfunction.
The diagnosis function of AVC-LAN varies depending on the master instrument.
(1)When the radio receiver assembly is master component
Service check mode
This is the mode to check any malfunction in each component with DTC
Detail information mode
This is the mode to check further details from the service check mode (The malfunction of the mutual relation between each component and the connected component can be checked)
(2)When the multi-display is master component
Service check mode
This is the mode to check any malfunction in each component with DTC
Display check mode
This is the mode to check any malfunction in multi-display with DTC
Navigation check mode
This is the mode to check any malfunction in navigation system with DTC
:
In the Audio signal, Video signal, and Control signal equipped with navigation system, the master component is multi-display.

5.Start up diagnosis mode
When the radio receiver assembly is master instrument
(1)Turn the audio off and then turn the ignition switch to the ACC position.
(2)While pressing preset switch “1″ and preset switch “6″ simultaneously, press the “CD” button three times.
(3)A beep sounds three times and the mode changes into service check mode.

1.General
This system maintains the vehicle at the speed the driver has set, as long as there are no vehicles in front in the same lane. If the system detects a vehicle being driven in front at a slower speed than one’s own vehicle while the driver is driving at a set speed, it closes the throttle valve to decelerate. If additional deceleration is necessary, it shifts the gears down to decelerate. If further deceleration is necessary, the system controls the brake actuator in order to apply the brakes. Then, the system maintains the vehicle-to-vehicle distance that has been set by the driver.
Thereafter, if there are no vehicles being driven in front within the set vehicle-to-vehicle distance because either the vehicle in front or one’s own vehicle has changed lanes, the system accelerates slowly to reach the set speed and resumes driving at the set speed.
2.Construction
(1)Laser radar sensor
There is a laser emitting portion, laser receiving portion, and the CPU in the laser radar sensor. The laser beams emitted by the laser emitting portion are radiated forward.
Then, the laser beams are reflected by the reflectors of the vehicle that is driven in front. The duration that the reflected beams return to the laser receiving portion is calculated by the CPU.
This sensor determines the distance between the vehicle and the vehicle in front. Then, it calculates the relative speed. These data are then transmitted to the distance control ECU. This sensor is designed so that it does not react to non-moving objects.
(2)Distance control ECU
Determines which vehicle to follow based on the information provided by the laser radar sensor, calculates the target acceleration signals for following the vehicle, and transmits an acceleration/deceleration request, shift-down request, warning buzzer request, and brake request to the engine and ECT ECU, and skid control ECU.