Control System

CONTROL SYSTEM

1. CALCULATION OF REQUIRED BLOW-OUT AIR TEMPERATURE (TAO)




1. REQUIRED BLOW-OUT AIR TEMPERATURE (TAO):
Upon reception of temperature set switch signals in addition to cabin temperature, ambient temperature and sunload sensor signals, the ECM calculates the TAO first and then, based on the calculated temperature, it determines the outlets from which the air is to be blown out.
2. CALCULATION OF REQUIRED TAO:
- When the set temperature is 18.0 °C, the TAO is fixed at the MAX COOL.
- When the set temperature is 32.0 °C, the TAO is fixed at the MAX HOT.
- When the set temperature is 18.5 °C to 31.5 °C, an optimum TAO is calculated based on the set temperature, as well as the cabin temperature, ambient temperature and sunload data at that time.




2. TEMPERATURE CONTROL
The temperature control is made based on the driver's inputs from the temperature set switch and the data from various temperature sensors; the ECM determines the TAO using these data and operates the air mix motor so that the TAO can be attained.
The ECM compares the air mix damper opening it has received from the air mix damper potentiometer with the target opening it has calculated and, if necessary, operates the motor to move the damper to the HOT or COLD side and hold the damper in an appropriate position.
The target damper opening is corrected using the sunlight intensity data.
The air mix damper is moved fully to the HOT side and held there when the temperature set switch is placed at the FULL HOT position (32 °C), while it is moved fully to the COLD side and held there when the switch is placed at the FULL COLD position (18 °C).

3. AIR FLOW CONTROL




- Normal air flow control:
When the air conditioning system is in the automatic control mode, the air flow is determined based on the TAO calculated by the ECM. The blower fan speed is controlled accordingly.
In the automatic control mode, the minimum air flow is different between DEF mode and the other modes. For the minimum air flow in BI-LEVEL, HEAT and DEF/HEAT modes, a voltage of 5.5 V is applied to the blower motor, while for the DEF mode a voltage of 9.0 V is applied.
The minimum air flow is corrected by the sunbeam intensity if the VENT or BI-LEVEL mode is selected.
- Blower fan starting speed control:
When the blower motor is turned ON in the automatic control mode, the fan speed is initially low and then gradually increases (applied voltage increases by 1 V every second until an appropriate voltage is reached) to prevent air from blowing out in a gust.
- Blower fan control at low coolant temperatures:
Even when the blower motor is automatically turned ON, the blower fan is kept stopped or allowed to rotate at the minimum speed for a maximum of 150 seconds depending on the cabin temperature and the ambient temperature, if the engine coolant temperature is below 49 °C with the air outlets for the VENT or DEF mode selected.
After the conditions for prohibiting blower fan operation or limiting its speed are removed, the voltage applied to the blower motor is increased gradually (by 0.34 V every minute) such that a large amount of cold air does not blow out toward the leg area.
Once the coolant temperature exceeds 49 °C, the normal blower fan control is performed including the starting speed control.
- Blower fan stop control with compressor ON:
The blower fan is stopped for 3 seconds if the compressor is turned ON with the intake sensor-detected temperature is higher than 35 °C.




4. AIR INLET CONTROL SYSTEM
The air inlet control system determines whether the air inlet damper is to be opened depending on the TAO calculated by the ECM, thus selecting either inside air recirculation or fresh air introduction
The damper is generally opened for fresh air introduction when the compressor is turned OFF.
It is also opened generally when the DEF position is selected.




5. AIR OUTLET CONTROL SYSTEM
The air outlet control system automatically selects the most appropriate air outlet combination depending on the ECM-calculated TAO by activating servo-motors for the VENT; BI-LEVEL or HEAT modes.
When the OFF switch is pressed position, the air outlet control system is held in the HEAT mode.




6. COMPRESSOR CONTROL SYSTEM
In the automatic air-conditioning mode, the A/C relay is activated or deactivated depending on the TAO (required blow-out air temperature), TAM (ambient temperature) and T INT (suction air temperature) to operate or stop the compressor.
The compressor operation circuit supplies current to the magnet clutch as the ECM activates the A/C relay by connecting its coil to the ground.




- Control by TAO and TAM




- Control by T INT