Isuzu N-Series. Manual - part 59

1B-6 AIR CONDITIONING

Evaporator

The evaporator (1) cools and dehumidifies the air before
the air enters the vehicle. High-pressure liquid refriger-
ant flows through the expansion valve into the low-pres-
sure area of the evaporator.The heat in the air passing
through the evaporator core is lost to the cooler surface
of the core, thereby cooling the air.
As heat is lost between the air and the evaporator core
surface, moisture in the vehicle condenses on the out-
side surface of the evaporator core and is drained off as
water.
When the evaporator malfunctions, the trouble will show
up as inadequate supply of cool air. The causes is typi-
cally a partially plugged core due to dirt, or a malfunc-
tioning blower motor.
The evaporator core with a laminate louver fin is a sin-
gle-sided tank type where only one tank is provided un-
der the core.

Expansion Valve

This expansion valve is external pressure type and it is
installed at the evaporator intake port.
The expansion valve converts the high pressure liquid
refrigerant sent from the receiver/drier to a low pressure
liquid refrigerant by forcing it through a tiny port before
sending it to the evaporator.
This type of expansion valve consists of a temperature
sensor, diaphragm, ball valve, ball seat, spring adjust-
ment screw, etc.
The temperature sensor contacts the evaporator outlet
pipe, and converts changes in temperature to pressure.
It then transmits these to the top chamber of the dia-
phragm.
The refrigerant pressure is transmitted to the dia-
phragms bottom chamber through the external equaliz-
ing pressure tube.
The ball valve is connected to the diaphragm. The open-
ing angle of the expansion valve is determined by the
force acting on the diaphragm and the spring pressure.
The expansion valve regulates the flow rate of the refrig-
erant. Accordingly, when a malfunction occurs to this ex-
pansion valve, both discharge and suction pressures
get low, resulting in insufficient cooling capacity of the
evaporator.
For R-134a air conditioning, the expansion valve cali-
bration has been changed from R-12 to match the R-
134a characteristics.

1

2

N1A0212E

N1A0050E

Legend

1. Expansion valve
2. Insulator
3. Evaporator core

N1A0051E

AIR CONDITIONING 1B-7

Electronic Thermostat

The thermostat consists of the thermosensor (1) and
thermostat unit (2) which functions electrically to reduce
the noises being generated while the system is in oper-
ation.
The electronic thermosensor is mounted at the evapora-
tor core outlet and senses the temperature of the cool air
from the evaporator, Temperature signals are input to
the thermostat unit. This information is compared by the
thermo unit and the results in output to operate the A/C
thermo relay and turn the magnetic clutch “ON” or “OFF”
to prevent evaporator freeze-up.
A characteristic of the sensor is that the resistance de-
creases as the temperature increases and the resis-
tance increases as the temperature decreases.

Refrigerant Line

Restrictions in the refrigerant line will be indicated by:

1. Suction line; A restricted suction line will cause low

suction pressure at the compressor, low discharge
pressure and little or not cooling.

2. Discharge line; A restriction in the discharge line

generally will cause the discharge line to leak.

3. Liquid line; A liquid line restriction will be evidenced

by low discharge and suction pressure and insuffi-
cient cooling.

Refrigerant flexible hoses that have a low permeability
to refrigerant and moisture are used.
These low permeability hoses have a special nylon layer
on the inside.

Service Charge Valves

R-134a service charge valve shapes is different from the
charge valves used in the R-12 system. The charging
hoses have a quick-joint type fitting, to reduce refriger-
ant loss during removal and installation. This type of
valve also eliminates the possibility of cross charging R-
12 and R-134a systems when using approved service
equipment.

N1A0052E

Legend

1. Reinforcement layer (Polyester)
2. External rubber layer
3. Internal rubber layer
4. Resin layer (Nylon)

N1A0053E

N1A0054E

1B-8 AIR CONDITIONING

Air Conditioning Parts

Except 4HK1-TC Engine Model For Australia

Legend

1. Evaporator

5. Refrigerant suction line

2. Compressor bracket

6. Receiver / drier

3. Compressor

7. Pressure switch

4. Refrigerant liquid line

8. Condenser

N1A0055E

3

2

1

8

6

4

5

7

AIR CONDITIONING 1B-9

4HK1-TC Engine Model For Australia

Legend

1. Evaporator

5. Refrigerant suction line

2. Compressor bracket

6. Receiver / drier

3. Compressor

7. Pressure switch

4. Refrigerant liquid line

8. Condenser

1

7

4

5

2

3

6

8

N1A0197E