Lexus SC300 / Lexus SC400. Service manual — part 13

OPERATION OF DAMPERS

AC–8

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AIR CONDITIONING SYSTEM

Description

CONTROL FUNCTIONS
Interior Room Temperature Control System

(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor, evaporator temperature

sensor and solar sensor) and the temperature setting, the air conditioner control ECU determines the air
flow volume and outputs signals to the air mix servomotor.

(c) When it receives signals from the ECU, the air mix servomotor opens or closes the air mix damper to

change the air flow temperature. When the temperature reaches the specified temperature, it is detected
by the air mix damper position sensor and the ECU stops the servomotor.

HINT: If the desired temperature setting is 65

°

F, the ECU forcedly sets the air mix damper to the Max Cool posi-

tion. If it is set at 85

°

F, the ECU forcedly sets the air mix damper to the Max Hot position.

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AIR CONDITIONING SYSTEM

Description

AC–9

Blower Fan Speed Control System

(When AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and the

temperature setting, the air conditioner control ECU determines the air flow volume and outputs signals
to the power transistor.

(c) When it receives signals from the ECU, the power transistor increases or reduces the blower motor speed

to control the air flow volume.

(When AUTO Switch is OFF)
The ECU turns the power transistor increasing or reducing the blower motor speed fixing the air flow volume
in accordance with the position of the Manual switch.

AC–10

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AIR CONDITIONING SYSTEM

Description

Air Flow Mode Control System

(When the AUTO Switch is ON)
(a) The desired temperature is set using the TEMP switch.
(b) From the input signals (room temperature sensor, ambient temperature sensor and solar sensor) and the

temperature setting, the air conditioner control ECU determines the air flow mode and outputs signals to
the mode servomotor and max cool servomotor.

(c) When it receives signals from the ECU, the servomotors open or close each of the dampers to change the

air flow mode.

(When the AUTO Switch is OFF)
The ECU fixes the air flow mode in accordance with the Manual switch position.
(When the Engine is Cold)
If the Mode is set on B/L or FOOT, the ECU forcedly changes the air vent to DEF if cold signals are input from
the water temperature sensor.

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AIR CONDITIONING SYSTEM

Description

AC–11