Isuzu N-Series. Service 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