Isuzu N-Series. Manual — part 46
SERVICE INFORMATION 00-15
Air Conditioning Cycle Troubleshooting
* For the execution of the charging and discharging operation in the table above, refer to the “RECOVERY, RECY-
CLING, EVACUATION AND CHARGING” in section 1B.
TROUBLE
POSSIBLE CAUSE
CORRECTION
No cooling or insufficient
cooling
1. Magnetic clutch does not run
• Refer to “MAGNETIC CLUTCH
TROUBLESHOOTING”
2. Compressor is not rotating property
• Drive belt loosened or broken
• Adjust the drive belt to the specified
tension or replace the drive belt
• Magnetic clutch face is not clean
and slips
• Clean the magnetic clutch face or re-
place
• Incorrect clearance between mag-
netic drive plate and pulley
• Adjust the clearance (Refer to Section
1D “COMPRESSOR OVERHAUL”)
• Compressor oil leaks from shaft
seal or shell
• Replace the compressor
• Compressor seized
• Replace the compressor
3. Insufficient or excessive charge of re-
frigerant
• Discharge and recover refrigerant.
Recharge to specified amount.
4. Leaks in the refrigerant system
• Check refrigerant system for leaks
and repair as necessary.
Discharge and recover refrigerant.
Recharge to specified amount.
5. Condenser clogged or insufficient ra-
diation
• Clean the condenser or replace as
necessary
• Check radiator or condenser fan func-
tion
6. Temperature control link unit of the
heater unit defective
• Repair the link unit
7. Unsteady operation due to foreign
substance in expansion valve
• Replace the expansion valve
8. Poor operation of electronic thermo-
stat
• Check electronic thermostat and re-
place as necessary
Insufficient velocity of
cooling air
1. Evaporator clogged or frosted
• Check evaporator core and replace or
clean the core
2. Air leaking from cooling unit or air duct
• Check evaporator and duct connec-
tion, then repair as necessary
3. Blower motor does not rotate properly
• Refer to “FAN SWITCH TROUBLE-
SHOOTING”
00-16 SERVICE INFORMATION
Checking Refrigerant System with Manifold
Gauge
Conditions;
• Ambient temperature at approx. 30 — 35
°C (86 —
95
°F)
• Run the engine at 1,500 rpm
• A/C switch is “ON”
• Run the blower motor at “4” (high) position
• Temperature control lever sets at “MAX COLD”
• Air source selector lever at “CIRC”
• Open then the all doors and engine hood
Normal pressures kPa (kg
⋅cm
2
/PSl)
• Low-pressure side: Approx. 127 — 245 (1.3 — 2.5/
18 — 36)
• High-pressure side: Approx. 1373 — 1667 (14 —
17/199 — 242)
Connect the manifold gauge
Low-pressure hose (LOW) - Suction side (1)
High-pressure hose (HI) - Discharge side (2)
Caution:
Vehicles that use Refrigerant-134a (R-134a) is used in
the air conditioning system, be sure to use manifold
gauges, charging hoses and other air conditioning ser-
vice tools for R-134a when checking the refrigerant sys-
tem. (Refer to “ON VEHICLE SERVICE” for Precautions
for R-134a Air Conditioning System in section 1B.)
Legend
1. Low side
2. High side
N1A0002E
SERVICE INFORMATION 00-17
* For the charging and discharging operations in the table above, refer to “RECOVERY, RECYCLING, EVACUATION
AND CHARGING” in section 1B.
RESULT
SYMPTOM
TROUBLE CAUSE
CORRECTION
Discharge (High)
pressure gauge
abnormally high
Reduced or no air flow through
the condenser
• Condenser clogged or dirty
• Radiator (condenser) fan
does not operate properly
• CIean
• Check cooling fan op-
eration
No bubbles in sight glass when
condenser is cooled by water
(Insufficient cooling)
• Excessive refrigerant in sys-
tem
• Check sight glass.
(See “Reading Sight
Glass”)
• Discharge and recover
refrigerant.
Recharge to specified
amount
After stopping air conditioning,
pressure drops approx. 196
kPa (2.0 kg
⋅cm
2
/28 PSl) quickly
• Air in system
• Evacuate and charge
refrigerant system
Discharge (High)
pressure gauge
abnormally low
Insufficient cooling and exces-
sive bubbles in the sight glass
• Insufficient refrigerant in
system
• Check sight glass.
(See “Reading Sight
Glass”)
• Check for leaks
• Discharge and recover
refrigerant.
Recharge to specified
amount
Low pressure gauge indicates
vacuum
• Clogged or defective expan-
sion valve
• Replace the expansion
valve
Frost or dew on refrigerant line
before and after receiver/ drier
or expansion valve, and low
pressure gauge indicates vac-
uum
• Restriction caused by de-
bris or moisture in receiver/
drier
• Check system for re-
striction and replace
receiver/drier
After turning off air condition-
ing, high and low pressure
gauge balanced quickly
• Compressor seal defective
• Poor compression due to
defective compressor gas-
ket
• Replace or repair com-
pressor
Suction (Low)
pressure gauge
abnormally high
Low pressure gauge is lowered
after condenser is cooled by
water
• Excessive refrigerant in sys-
tem
• Discharge and recover
refrigerant
Recharge to specified
amount
Low pressure hose tempera-
ture around the compressor
refrigerant line connector is
lower than around evaporator
• Unsatisfactory valve opera-
tion due to defective tem-
perature sensor of
expansion valve
• Expansion valve opens too
long
• Replace the expansion
valve
After turning off air condition-
ing, high and low pressure
gauge is balanced quickly
• Compressor gasket is de-
fective
• Replace
Air conditioning turns off before
passenger compartment is suf-
ficiently cool
• Electronic thermostat defec-
tive
• Check the electronic
thermostat and replace
as necessary
00-18 SERVICE INFORMATION
RESULT
SYMPTOM
TROUBLE CAUSE
CORRECTION
Suction (Low)
pressure abnor-
mally low
Condenser is not hot and
excessive bubble in sight glass
• Insufficient refrigerant
• Check sight glass.
(See “Reading Sight
Glass”)
• Check for leaks
• Discharge and recover
refrigerant.
Recharge to specified
amount
Frost on the expansion valve
inlet line
• Expansion valve clogged
• Replace the expansion
valve
A distinct difference in temper-
ature between the inlet and
outlet refrigerant lines of the
receiver/drier
• Receiver/drier clogged
• Replace the receiver/
drier
Expansion valve outlet refriger-
ant line is not cold and low-
pressure gauge indicates vac-
uum
• The temperature sensor of
the expansion valve is de-
fective, and the valve can-
not regulate the correct flow
of the refrigerant
• Replace the expansion
valve
Discharge temperature is low
and air flow from vents is
restricted
• Frozen evaporator core fins
• Check electronic ther-
mostat and replace as
necessary
Low-pressure gauge reading is
low, or a vacuum reading may
be shown
• Clogged or blocked refriger-
ant line
• Replace refrigerant line
Suction (Low)
and Discharge
(High) pressure
abnormally high
No bubbles in sight glass after
condenser is cooled by water
(Insufficient cooling)
• Excessive refrigerant in sys-
tem
• Check sight glass.
(See “Reading Sight
Glass”)
• Discharge and recover
refrigerant.
Recharge to specified
amount
Reduce air flow through con-
denser
• Condenser clogged
• Radiator (condenser) fan
does not rotate properly
• Clean
• Check cooling fan op-
eration
Suction (Low) pressure hose is
not cold
• Air in system
• Evacuate and charge
refrigerant
Suction (Low)
and Discharge
(High) pressure
abnormally low
Insufficient cooling and exces-
sive bubbles in the sight glass
• Insufficient refrigerant in
system
• Check sight glass.
(See “Reading Sight
Glass”)
• Check for leaks
• Discharge and recover
refrigerant.
Recharge to specified
amount
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