Lexus ES300 (1997 year). Manual - part 25

98

BODY ELECTRICAL — AIR CONDITIONING



 CONSTRUCTION AND OPERATION

1. Heater Control Panel



An easy-to-use dial and push button type heater control panel is used.



The size and the position of the buttons are designed with the frequency of use and the order of operation
controls is taken into account.



The heater control panel uses a larger LCD (Liquid Crystal Display) to display the set temperature, air
outlet status, etc., and improves its visibility.



The set temperature display and the outside temperature display on the heater control panel can be
switched by the push of a button.

2. Air Conditioning Unit

As in the previous model, the air conditioning unit incorporates a blower, heater and cooler units. This
provides high rigidity and lower ventilating resistance.

Heater Core

A lightweight aluminum heater core is used on all models.

3. Condenser

As in the previous model, the 3-passage flow type condenser which has a greater heat exchanging capability
has been adopted on all models.

4. Defroster Nozzle

The front defroster nozzle inner wall is modified into a radial configuration for a smoother air flow.

99

BODY ELECTRICAL — AIR CONDITIONING

5. Solar Sensor

As in the previous model, a dome-type solar sensor is used. However, in the new model, the sensor is made
compact for improved appearance, and the orientation of the light is improved through the lens cutting
process. As a result, the air-conditioning control capabilities while under diagonal solar radiation are
improved.

6. Air Conditioning ECU

The following table is a comparison of the air conditioning ECU functions between the new and previous
model.

System

Function

New

Previous

Calculation of
Required Outlet Air
Temperature

Calculates the required outlet air temperature based on
the set temperature, room air temperature, ambient air
temperature and solar radiation.

Temperature Control

To drive the air mix servomotor in accordance with the
required outlet air temperature, the air temperature
passed through the evaporator and the engine coolant
temperature and to control the outlet air temperature
(Air Mix Damper Control).

Sets the blower speed according to operation of the
blower switch (Manual Control).

(5-step)

(5-step)

Blower Control

When the automatic control or front defroster switch is
turned on, the blower starts. Then the blower speed
that is appropriate for the required outlet air
temperature
is compared with the blower speed that is appropriate
for solar radiation, and the blower is controlled with the
faster speed of the above two speeds (Automatic
Control). However, when the coolant temperature is
below a predetermined level and the air outlet is in the
“foot” or “bi-level” mode, the blower will not operate
(Warm-Up Control).

100

BODY ELECTRICAL — AIR CONDITIONING

System

Function

New

Previous

Blower Control

When the air outlet mode is at “face” or “bi-level” and
the required outlet air temperature is below a
predetermined level, the blower is set to operate after a
time lag in order to prevent hot air from being blown
out suddenly right after the engine is started
(Time-Lagged Air Flow Control).

Drives the air inlet servomotor according to the
operation of the air inlet control switch and fixes the
dampers in the “fresh” or “recirc.” position (Manual
Control).

Air inlet Control

Switches the damper position between “fresh”, “fresh
and recirc. mix” or “recirc.” according to the required
outlet air temperature (Automatic Control).

Fixes the damper position on “fresh” if the front
defroster switch is turned on during automatic control
(Forced Fresh Air Intake Control).

Drives the air outlet step motor in accordance with the
operation of the mode select and front defroster
switches and fixes the dampers in the “face”, “bi-level”,
“foot”, “foot and def.” or “def.” position (Manual
Control).

Air Outlet Control

Switches the damper position between “face”,
“bi-level” of “foot” according to the required outlet air
temperature (Automatic Control)

If the blower is under warm-up control when the air
outlet mode is in “bi-level” or “foot” mode, the LCD
display remains as it is while the air outlet step motor is
driven and the dampers are switched to the “def.”
position, preventing cool air from leaking from the foot
vent (Def.-Foot Control).

101

BODY ELECTRICAL — AIR CONDITIONING

System

Function

New

Previous

If the A/C switch is switched on while the blower is
turned on, this turns on the magnetic clutch relay and
operates the compressor (Manual Control).

When the AUTO switch is pressed, the magnetic clutch
relay is turned on. (Automatic Control).

Switches the magnetic clutch relay off when the engine
speed is below 450 rpm, when the blower is turned off
by the warm-up control, or when the refrigerant
pressure is abnormally high or low (Abnormal
Condition Detection).

Compressor
Control

Switches the magnetic clutch relay on regardless of the
operating condition of the A/C and automatic control
switches if the front defroster switch and blower are
turned on (Def. Linked Control).

Compares the engine speed and compressor speed. If it
is judged that the compressor is locked, the magnetic
clutch relay goes off and the A]C switch indicator light
blinks to warm the driver (Compressor Lock Detection).

If the temperature of the air immediately after having
passed through the evaporator is detected by the
thermistor to be below 3

C (37.4F), the magnetic

clutch relay is turned off (Low Temperature Control).

In order to maintain engine condition, the magnetic
clutch relay operation is delayed for predetermined time
after the A/C switch is turned on (Compressor Delay
Control).

Rear Defogger
Control

Switches the rear defogger on for 15 minutes when the
rear defogger switch is switched on. Switches the rear
defogger off if the switch is pressed while it is
operating.

Checks the sensors in accordance with operation of the
air conditioning switches, then displays a code No. to
indicate if there is a malfunction or not (Sensor Check
Function).

—

Self-Diagnosis

Checks the sensors in accordance with operation of the
air conditioning switches, then displays a code No. and
sounds a buzzer to indicate if there is a malfunction or
not (Sensor Check Function).

—

Drives the actuators through a predetermined sequence
in accordance with the operation of the air conditioning
switches (Actuator Check Function).