System Description

WARNING: This page is about a different car, the 2007 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.

SYSTEM CONTROL

CONTROL OUTLINE CHART

Control	Outline
Required Outlet Air Temperature	Calculation Calculates the required outlet air temperatures for driver side and front passenger side based primarily on inputs of temperature control switches signals (driver and front passenger sides), room temperature signal, ambient temperature signal and solar sensor signal.
Retractable Hardtop Open A/C Control	Actuates foot servo motor when retractable hardtop is open in order to blow air out of lap-jet. Automatically corrects blower airflow volume in accordance with vehicle speed when retractable hardtop is open. Varies solar correction volume in accordance with ambient temperature when retractable hardtop is open. Automatically cancels room temperature signals and effects automatic air conditioning control when the retractable hardtop is open.
Outlet Air Temperature Control	Determines outlet air temperature by adding evaporator temperature signal correction to required outlet air temperature, and actuates air mix servo motor.
Blower Control	Controls airflow volume in multiple steps in accordance with amount of sunlight. Stops blower fan until engine coolant temperature increases to prescribed temperature when air outlet is in FOOT or BI-LEVEL mode and engine coolant temperature is low. Stops blower fan for approximately 4 seconds, turns compressor ON to cool air conditioning unit, then raises blower fan speed in steps to attain target airflow volume, when air outlet is in FACE or BI-LEVEL mode and evaporator temperature is high (30°C minimum). Increases the blower's minimum flow volume if a strong sunlight is indicated by solar sensor signal, and decreases blower's minimum flow volume if a weak sunlight is indicated, when air outlet is in FACE or BI-LEVEL mode.
Air Outlet Control	Actuates mode servo motor in accordance with mode ratio that is calculated from required outlet air temperature and automatically switches the air outlet modes (FACE, BI-LEVEL, or FOOT).
Air Inlet Control	Actuates air inlet servo motor in accordance with driver side required outlet air temperature to automatically switch between RECIRCULATION and FRESH air inlet modes.
Compressor Control	Determines the compressor has locked if slippage rate of drive belt exceeds 80% for 3 seconds or more while magnet clutch is ON, turns OFF magnet clutch, and blinks indicator lamp of A/C control switch. (This control is not effected when engine speed is below 450 rpm.) Detects refrigerant pressure in accordance with signals from A/C pressure switch, and turns OFF magnet clutch if there is a malfunction. Turns magnet clutch OFF and prevents evaporator from frosting when evaporator temperature is below -4°C (25°F). Turns magnet clutch ON / OFF in accordance with ambient temperature, when air inlet is in the FRESH mode. Automatically turns ON magnet clutch when the user sets the air outlet to DEF mode.
Outer Temperature Indication Control	Based on the signals from ambient temperature sensor, this control calculates outside temperature, which is then corrected in A/C amplifier, and shown in A/C control panel.
Automatic Recirculation Control	A/C amplifier automatically controls air inlets based on signals from smog ventilation sensor.
Self-diagnosis (Panel Diagnosis)	Checks sensor in accordance with operation of A/C switches, then LCD on A/C control panel displays a DTC (Diagnosis Trouble Code) to indicate if there is a malfunction or not (sensor check function). Drives actuators through a predetermined sequence in accordance with operation of A/C switches (actuator check function).