Lexus RX300 (MCU15). Service manual — part 64

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BODY ELECTRICAL — AIR CONDITIONER

129

Sub-Cool Cycle

In the sub-cool cycle of the sub-cool condenser that has been adopted, after the refrigerant passes through
the condensing portion of the condenser, both the liquid refrigerant and the gaseous refrigerant that could
not be liquefied are cooled again in the super-cooling portion. Thus, the refrigerant is sent to the evaporator
in an almost completely liquefied state.

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Multi-Flow Condenser

Condensing Portion

Liquid
Refrigerant

Super-Cooling Portion

Modulator

Gaseous
Refrigerant

NOTE:

The point at which the air bubbles disappear in the refrigerant of the sub-cool cycle is lower than
the proper amount of refrigerant with which the system must be filled. Therefore, if the system
is recharged with refrigerant based on the point at which the air bubbles disappear, the amount
of refrigerant would be insufficient. As a result, the cooling performance of the system will be
affected.
For the proper method of verifying the amount of the refrigerant and to recharge the system with
refrigerant, see the LEXUS RX300 Repair Manual (Pub. No. RM785E).

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High

Pressure

Properly Recharged Amount

Point in which Bubbles Disappear

Amount of Refrigerant

BODY ELECTRICAL — AIR CONDITIONER

Service Tip

The replacement interval for the clean air filter is 30,000 km.
However, it varies with the use conditions (or environment).

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4. Compressor

A compact, lightweight, and low-noise swash plate type compressor has been adopted on the RX300.

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Swash Plate

Piston

Shaft

Swash Plate Chamber

5. Clean Air Filter

A clean air filter that excels in removing pollen and dust is optional equipment.
This filter, which cleans the air in the cabin, is made of polyester. Thus, it can be disposed of easily as
a combustible material, a feature that is provided in consideration of the environment.
To facilitate the replacement of the filter, a one-touch clip is used in the filter cover which is unified with
filter case. Thus, a construction that excels in serviceability has been realized.

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Clean Air
Filter

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BODY ELECTRICAL — AIR CONDITIONER

131

6. Air Conditioner ECU

General

Air conditioner ECU is built in combination meter. The automatic controlled type air conditioner system
has following control.

Control

Outline

Outlet Air Temperature Control

In response to the temperature control switch setting, the required
outlet air temperature, evaporator temperature sensor, and water
temperature sensor compensations are used by the air mix control
damper control to calculate a tentative damper opening angle,
through an arithmetic circuit in the air mix damper, to arrive at a tar-
get damper opening angle.

Blower Control

This function controls the operation of the blower motor in accor-
dance with the signals from the water temperature sensor, evapora-
tor temperature sensor, and the solar sensor. In addition, it protects
the blower motor controller from the sudden drive current that oc-
curs when the blower motor is activated.

Air Outlet Control

When the AUTO switch has been turned ON, automatic control
causes the servomotor (for air mix control) to rotate to a desired
position in accordance with the target damper opening, which is
based on the calculation of the required outlet air temperature. Fur-
thermore, under automatic control, the potentionmeter in the servo-
motor (for air mix control) is used to detect the actual damper open-
ing, as opposed to the calculated target damper opening, so that
control can be effected to match the actual damper opening to the
calculated target damper opening.

Air Inlet Control

Drives the servomotor (for air inlet) according to the operation of
the air inlet control switch and fixes the dampers in the FRESH or
RECIRC position.

Compressor Control

This control turns OFF the magnetic clutch of the compressor when
the blower motor is turned OFF at the time the water temperature
is below a predetermined value, an abnormal refrigerant pressure
has been input, or the discharge temperature of the evaporator is be-
low a predetermined value.

Rear Window Defogger Control

Switches the rear defogger and outside rear view mirror heaters on
for 15 minutes when the rear defogger switch is switched on.
Switches them off if the switch is pressed while they are operating.

Outer Temperature Indication

Control

Based on the signals from the ambient temperature sensor, this con-
trol calculates the outside temperature, which is then corrected in
the air conditioner ECU, and shown in the multi display.

Self-diagnosis

Checks the sensors in accordance with operation of the air condi-
tioner switches, then multi display a DTC (Diagnosis Trouble
Code) to indicate if there is a malfunction or not (sensor check func-
tion).

g

Drives the actuators through a predetermined sequence in accor-
dance with the operation of the air conditioner switches (actuator
check function).

BODY ELECTRICAL — AIR CONDITIONER

132

Self-Diagnosis

D The air conditioner ECU has a self-diagnosis function. It stores any operation failures in the air condition-

er system memory in the form of a malfunction code. By operating switches on the air conditioner control
switches, the stored malfunction code will be indicated. Since diagnostic results are stored directly by
electric power from the battery, they are not cleared even when the ignition switch is turned off.

" Functions A

Function

Outline

Indicator Check

Checks indicator lights and temperature setting display.

Sensor Check

Checks the past and present malfunctions of the sensors, and
clearing the past malfunction data.

Actuator Check

Checks against actuator check pattern if blower motor, servo
motors and magnetic clutch are operating correctly according
to signals from ECU.

D The check functions can be started by the following procedure shown below.

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Indicates a switch operation

Turn ignition switch ON with
AUTO and R/F switches held
down.

Indicator Check

OFF

OFF

OFF

OFF

Sensor Check

Continuous

Operation

DEF

DEF

DEF

DEF

Sensor Check

(Stepped Operation)

R/F

R/F

R/F

AUTO

AUTO

AUTO

If both AUTO and R/F
switches are not pressed
at the same time.

Cancel check Mode

(normal operation now possible)

Actuator Check

(Stepped Operation)

Actuator Check

Continuous

Operation

For details on the indicator check, sensor check, actuator check function, and clearing of this system,
refer to the LEXUS RX300 Repair Manual (Pub. No. RM785E).