Lexus RX300 (MCU15). Manual - part 84

I01386

AC–4

–

AIR CONDITIONING

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

2.

INSPECT REFRIGERANT PRESSURE WITH MAN-
IFOLD GAUGE SET

This is a method in which the trouble is located by using a man-
ifold gauge set. Read the manifold gauge pressure when these
conditions are established.
Test conditions:

S

Temperature at the air inlet with the switch set at RECIRC
is 30 – 35 

°C (86 – 95 °F)

S

Engine running at 2,000 rpm

S

Blower speed control switch at ”HI” position

S

Temperature control dial on ”COOL” position

HINT:
It should be noted that the gauge indications may vary slightly
due to ambient temperature conditions.

(1)

Normally functioning refrigeration system.

Gauge reading:
Low pressure side:
0.15 – 0.25 MPa (1.5 – 2.5 kgf/cm

2

)

High pressure side:
1.37 – 1.57 MPa (14 – 15 kgf/cm

2)

I01387

Condition : Periodically cools and then fails to cool

I01388

Condition: Insufficient cooling

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AIR CONDITIONING

AIR CONDITIONING SYSTEM

AC–5

LEXUS RX300   (RM785E)

(2)

Moisture present in refrigeration system.

Symptom seen in 

refrigeration system

Probable cause

Diagnosis

Remedy

During operation, pressure on low

pressure side sometimes become

a vacuum and sometime normal

Moisture entered in refrigeration

system freezes at expansion valve

orifice and temporarily stops cycle,

but normal state is restored after a

time when the ice melts

S Drier in oversaturated state

S Moisture in refrigeration system

freezes at expansion valve orifice

and blocks circulation of refriger-

ant

(1) Replace condenser

(2) Remove moisture in cycle

through repeatedly evacuating air

(3) Charge proper amount of new

refrigerant

(3)

Insufficient cooling

Symptom seen in 

refrigeration system

Probable cause

Diagnosis

Remedy

S Pressure low on both low and

high pressure sides

S Bubbles seen in sight glass con-

tinuously

S Insufficient cooling performance

Gas leakage at some place in re-

frigeration system

S Insufficient refrigerant in system

S Refrigerant leaking

(1) Check for gas leakage with gas

leak detector and repair if neces-

sary

(2) Charge proper amount of re-

frigerant

(3) If indicated pressure value is

near 0 when connected to gauge,

create the vacuum after inspecting

and repairing the location of the

leak

I01389

Condition: Insufficient cooling

I01449

Condition: Does not cool (Cools from time to time in some cases)

AC–6

–

AIR CONDITIONING

AIR CONDITIONING SYSTEM

LEXUS RX300   (RM785E)

(4)

Poor circulation of refrigerant

Symptom seen in 

refrigeration system

Probable cause

Diagnosis

Remedy

S Pressure low in both low and

high pressure sides

S Frost on tube from condenser to

unit

Refrigerant flow obstructed by dirt

in condenser

condenser clogged

Replace condenser

(5)

Refrigerant does not circulate

Symptom seen in 

refrigeration system

Probable cause

Diagnosis

Remedy

S Vacuum indicated on low pres-

sure side, very low pressure indi-

cated on high pressure side

S Frost or dew seen on piping be-

fore and after condenser/ drier or

expansion valve

S Refrigerant flow obstructed by

moisture or dirt in refrigeration sys-

tem

S Refrigerant flow obstructed by

gas leakage from expansion valve

Refrigerant does not circulate

(1) Check expansion valve

(2) Clean out dirt in expansion

valve by blowing with air

(3) Replace condenser

(4) Evacuate air and charge new

refrigerant to proper amount

(5) For gas leakage from expan-

sion valve, replace expansion

valve

I01390

Condition: Insufficient cooling

I01392

Condition: Insufficient cooling

NOTE : These gauge indica-
tions are shown when the
refrigeration system has
been opened and the refrig-
erant charged without vacu-
um purging.

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AIR CONDITIONING

AIR CONDITIONING SYSTEM

AC–7

LEXUS RX300   (RM785E)

(6)

Refrigerant overcharged or insufficient cooling of
condenser

Symptom seen in 

refrigeration system

Probable cause

Diagnosis

Remedy

S Pressure too high on both low

and high pressure sides

S No air bubbles seen through the

sight glass even when the engine

rpm is lowered

S Unable to develop sufficient per-

formance due to excessive refrig-

eration system

S Insufficient cooling of condenser

S Excessive refrigerant in 

cycle → refrigerant over charged

S Condenser cooling → condenser

fins clogged of condenser fan

faulty

(1) Clean condenser

(2) Check condenser fan motor

operation

(3) If (1) and (2) are in normal

state, check amount of refrigerant

Charge proper amount of refriger-

ant

(7)

Air present in refrigeration system

Symptom seen in 

refrigeration system

Probable cause

Diagnosis

Remedy

S Pressure too high on both low

and high pressure sides

S The low pressure piping hot to

touch

S Bubbles seen in sight glass

Air entered in refrigeration system

S Air present in refrigeration sys-

tem

S Insufficient vacuum purging

(1) Check compressor oil to see if

it is dirty or insufficient

(2) Evacuate air and charge new

refrigerant