LEXUS SC300 1991 Service Repair Manual

Check voltage between terminal SET 1 ~ 5 and SG of A/C control
assembly
(1) Remove A/C control assembly with connec-tors.(See page AC-138).
(2) Turn ignition switch ON.
Measure voltage between terminals SET 1 ~ 5 and
SG of temp. control switch is turned from most left to
right position.
for USA spec.for Canada spec.
Proceed to next circuit inspection shown on
matrix chart. ( See page AC-36).
Go to step (2).
INSPECTION PROCEDURE
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Check temp. control switch.
Disconnect temp. control switch connector.
Measure resistance between terminals SET 1 ~ 5
and SG of temp. control switch is turned from most
left to right position.
for USA spec.for Canada spec.
Replace temp. control switch.
Check for open and short in harness and connector between A/C control
assembly and temp. control switch (See page IN-27).
Repair or replace harness or connector.
Check and replace A/C control assembly.
AC±94±
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Automatic Control Switch Circuit
CIRCUIT DESCRIPTION
The SW contact is ON while the automatic control SW is pushed, and
turns OFF when automatic control SW is released. When the SW is
turned
ON, the voltage at the SAUTO terminal of A/C control assem-
bly is almost 0 V and the ECU begins fully automatic control of the
blower speed, air inlet, air outlet and compressor operation.
DIAGNOSTIC CHART
Check voltage between terminal SAUTO
and SG of A/C control assembly.
Check automatic control SW.
Check for open and short in harness and
connector between automatic control SW
and ECU.
Check and replace A/C control assembly.
Proceed to next circuit inspection on
matrix chart(See page AC-36).
Replace automatic control SW.
Repair or replace harness or
connector.
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Check voltage between terminal SAUTO and SG of A/C control
assembly.
(2) Remove A/C control assembly with connectorsstill connected.
Proceed to next circuit inspection shown on
matrix chart. ( See page AC-36).
(3) Turn ignition switch on.
(1) Remove console upper panel. (See page
BO±111 ).
Measure voltage between terminal SAUTO and Sg
of A/C control assembly when automatic control SW
is operated.
Disconnect automatic control switch connector.
Measure resistance between terminal and of auto-
matic control switch connector when it is is
operated.
Replace automatic control switch.
Check automatic control switch.
Check for open and short in harness and connector between switch and
A/C control assembly (See page IN-27).
Repair or replace harness or connector.
Check and replace A/C control assembly.
INSPECTION PROCEDURE
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Diagnosis Circuit
CIRCUIT DESCRIPTION
This circuit sends signals to the A/C control assembly requesting output of \
diagnostic codes.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check voltage between terminals Tc and
E1 of TDCL.
Check harness and connector between air
conditioner control assembly and TDCL and
body ground.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36
).
Repair or replace harness or
connector.
Check and replace air conditioner control
assembly.
AC±98±
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Check voltage between terminal Tc and E1 of TDCL.
(2) Check voltage between terminals Tc and E1 of TDCL.
Voltage: 10 ± 14 V
(1) Turn ignition switch on.
Proceed to next circuit inspection shown on
matrix chart. ( See page AC-36).
Check for open and short in harness and connector between air conditioner con-
trol assembly and TDCL, TDCL and body ground.(See page IN-27).
Repair or replace harness or connector.
Check and replace air conditioner control
assembly.
INSPECTION PROCEDURE
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No.Gauge reading kPa (kgf/cm2, psi)ConditionProbable cause Remedy
LO: 1.5 ± 2.0(21 ±28, 147 ±196)
HI: 14.5 ± 15.0(206 ±213, 1422 ±1471)
Normal coolingNormally functioning
system
During operation, pressure at low
pressure side sometimes becomes a
vacuum and sometimes normal.Periodically cools
and then fails to
cool.Moisture present in
refrigeration system.(1). Replace receiver
(2). Remove moisturein system through
repeatedly
evacuating air
Inspection of Refrigeration System with Manifold Gauge Set
This is a method in which the trouble is located by using a manifold gauge s\
et. (See ºInstallation of Manifold
Gauge Setº on page AC±15) Read the manifold gauge pressure when the following conditions are es\
tablished:
(a) Temperature at the air inlet with the switch set at RECIRC is 30±35 °C (86±95 °F).
(b) Engine running at 2,000 rpm.
(c) Blower fan speed control switch set at high speed.
(d) Temperature control switch set at max. cool side.
HINT: It should be noted that the gauge indications may vary slightly due to\
ambient temperature conditions.
NOTICE:
w Always recover refrigerant before removing the parts in the refrigerant \
line and evacuating air.
w Evacuate air and charge proper amount of purified refrigerant after installing th\
e parts in the
refrigerant line.
AC±100
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No.Gauge reading kPa (kgf/cm2, psi)ConditionProbable causeRemedy
Pressure low at both low and high
pressure sides
Pressure too high at both low and
high pressure sides

Insufficient cooling

Bubbles seen in
sight glass

Insufficient cooling

Frost on tubes from
receiver to
unit
Replace receiver
Insufficient refrigerant(1) Check for gas
leakage with gas
leak tester and
repair if
necessary
(2) Add refrigerant
until bubbles
disappear
Refrigerant flow
obstructed by dirt in
receiver
Insufficient coolingInsufficient cooling of
condenser(1). Clean condenser
(2). Check fan motoroperation
(1). Check amount ofrefrigerant
If refrigerant is
overcharged
(2). Recover refrigeran
t
(3). Evacuate air and charge proper
amount of purified
refrigerant
Refrigerant
overcharged
(1). Replace receiver
(2). Check compres- sor oil to see if
dirtyAir present in system

Insufficient cooling

Frost in Large
amount of dew on
piping at low
pressure side Expansion valve
improperly mounted,
heat sensing tube
defective
(Open too wide)(1) Check heat sensing
tube installation
condition
If (1) is normal
(2) Check expansion valve and replace
if defective
(3). Remove air insystem through
repeatedly
evacuating air
NOTICE:
wAlways recover refrigerant before removing the parts in the refrigerant line a\
nd evacuating air.
w Evacuate air and charge proper amount of purified refrigerant after installing th\
e parts in the
refrigerant line.
HINT at 6:
These gauge indication are for when the refrigeration system has been op\
ened and the refrigerant charged
without evacuating air.
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No.Gauge reading kPa (kgf/cm2, psi)ConditionProbable causeRemedy
Vacuum indicated at low pressure
side, very low pressure indicated at
high pressure.
Pressure too high at low pressure
sides, pressure too low at high
pressure side.
Refrigerant does not
circulate
Does not cool(Cools from time
to time in some
cases)

Frost or dew seen
on piping before
and after receiver
or expansion
valve
(1) Check heat sensing
tube for gas
leakage and
replace expansion
If (1) is normal
(2) Clean out dirt in expansion valve by
blowing with air if
not able to remove
dirt replace
expansion valve
(3) Replace receiver
Does not coolInsufficient
compressionRepair or replace
compressor
NOTICE:
w Always recover refrigerant before removing the parts in the refrigerant line a\
nd evacuating air.
w Evacuate air and charge proper amount of purified refrigerant after installing th\
e parts in the
refrigerant line.
AC±102
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REFRIGERANT VOLUME
INSPECTION OF REFRIGERANT
VOLUME
1. RUN ENGINE AT IDLE SPEED
2. OPERATE A/C AT MAXIMUM COOLING FOR A FEWMINUTES
3. INSPECT AMOUNT OF REFRIGERANT Observe the sight glass on the liquid tube.
ItemSymptomAmount of refrigerantRemedy
1
Bubbles present in sight glassInsufficient*(1) Check for gas leakage with
gas leak tester and repair
if necessary
(2) Add refrigerant until bubbles disappear
2No bubbles present in sight
glassNone, sufficient or too muchRefer to items 3 and 4
3
No temperature difference
between compressor inlet and
outletEmpty or nearly empty(1) Check for gas leakage withgas leak tester and repair
if necessary
(2) Add refrigerant until bubbles disappear
4
Temperature between
compressor inlet and outlet is
noticeably differentProper or too muchRefer to items 5 and 6
5
Immediately after air conditioner
is turned off, refrigerant in sight
glass stays clearToo much(1) Recover refrigerant
(2) Evacuate air and charge
proper amount of
purified refrigerant
6
When air conditioner is turned
off, refrigerant foams and then
stay clearProper
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*: Bubbles in the sight glass with ambient temperatures higher can be cons\
idered normal if cooling is sufficient.
REFRIGERANT CHARGE VOLUME
Specified amount: 950 + 50 g (33.44 + 1.76 oz)
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AIR CONDITIONING SYSTEM Refrigerant VolumeAC±103
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