1995 ISUZU TROOPER Workshop Manual

The refrigeration cycle includes the following four
processes as the refrigerant changes repeatedly
from liquid to gas and back to liquid while circulat­
ing.
EVAPORATION
The refrigerant is changed from a liquid to a gas in­
side
the evaporator. The refrigerant mist that enters
the evaporator vaporizes readily. The liquid refrige­
rant removes
the required quantity of heat (latent
heat of vaporization) from the air around the evap­
orator core cooling fins and rapidly vaporizes.
Removing the heat cools the air, which is then
radiated
from the fins and lowers the temperature of
the air inside the vehicle.
The refrigerant liquid sent from the expansion valve
and the vaporized refrigerant gas are both present
inside the
evaporator and the liquid is converted to
gas.
With this change from liquid to gas, the pressure
inside
the evaporator must be kept low enough for
vaporization to occur at a lower temperature.
Because of that, the vaporized refrigerant is sucked
into the compressor.
COMPRESSION
The refrigerant is compressed by the compressor
until it is easily liquefied at normal temperature.
The vaporized
refrigerant in the evaporator is sucked
into the compressor. This action maintains the
refrigerant inside the evaporator at a low pressure
so
that it can easily vaporize, even at low tempera­
tures close to ooc (32°F).
Also, the refrigerant sucked into the compressor is
compressed inside the
cylinder to increase the
pressure and temperature to values such that the
refrigerant can easily liquefy at normal ambient
temperatures.
CONDENSATION
The refrigerant inside the condenser is cooled by the
outside air and changes from gas to liquid.
The high temperature, high pressure gas coming
from the compressor is cooled and liquefied by the
condenser with outside air and accumulated in the
receiver/drier. The heat radiated to the outside air by
the high temperature, high pressure gas in the
compressor is called heat of condensation. This is
the total quantity of heat (heat of vaporization) the
refrigerant removes
from the vehicle interior via the
evaporator and the work (calculated as the quantity
of heat) performed for compression.
'-' EXPANSION
The expansion valve lowers the pressure of the
refrigerant liquid so that it can easily vaporize.
AIR CONDITIONING 1 B -3
The process of lowering the pressure to encourage
vaporization before the
liquefied refrigerant is sent
to the evaporator is called expansion. In addition,
the expansion valve controls the flow rate of the
refrigerant liquid while decreasing the pressure.
That is, the quantity of refrigerant liquid vaporized
inside
the evaporator is determined by the quantity
of heat which must be removed at a prescribed
vaporization temperature.
It is important that the
quantity of refrigerant be controlled to exactly the
right value.
COMPRESSOR
It compressor performs two main functions:
It compresses low-pressure and low-temperature
refrigerant vapor from the evaporator into high­
pressure and high-temperature
refrigerant vapor to
the condenser. And it pumps refrigerant and
refrigerant
oil through the air conditioning system.
This vehicle is equipped with five-vane rotary com­
pressor.
The
thermo sensor is installed to the front head of
the compressor to protect it by stopping its
operation when the refrigerant gas is insufficient or
when the temperature is abnormally high.
• OFF ...... 160 ±soc (320.0 ± 9.0°F)
• ON
...... 135 ±soc (27S.O ± 9.0°F)
The specified amount of the compressor oil is 1SOcc
(S.O fl.oz.).
The oil used in the HFC-134a system compressor
differs from that used in R-12 systems.
Also, compressor oil to be used varies according to
the compressor model. Be sure to avoid mixing two
or more different types of oil.
If the wrong oil is used, lubrication will be poor and
the compressor will seize or malfunction.
The magnetic clutch connector is a waterproof
type.
MAGNETIC CLUTCH
The compressor is driven by the drive belt from the
crank
pulley of the engine. If the compressor is ac­
tivated each
time the engine is started, this causes
too much load to the engine. The magnetic clutch
transmits the power from the engine to the com­
pressor and activates it when the air conditioning is
"ON". Also, it cuts off the power from the engine to
the compressor when the air conditioning is "OFF".
(Magnetic clutch repair procedure can be found in
Section 1 D.)

1 B - 4 AIR CONDITIONING
Compressor
Thermosensor
Magnetic clutch
Fig. 18-2
CONDENSER
The condenser assembly is located in front of the
radiator. It carries the refrigerant and cooling fins to
provide rapid transfer of heat.
Also, it functions to cool and liquefy the high­
pressure and high-temperature vapor sent from the
compressor by the radiator fan or outside air.
A condenser
may malfunction in two ways: it may
leak, or it may be restricted. A condenser restric­
tion will result in excessive compressor discharge
pressure.
If a partial restriction is present, the
refrigerant expands after passing through the
restriction.
Thus, ice
or frost may from immediately after the
restriction. If air flow through the condenser or
radiator is blocked, high discharge pressures will
result. During normal condenser operation, the re­
frigerant outlet line will be slightly cooler than the
inlet line.
The vehicle is equipped with the parallel flow type
condenser. A larger thermal transmission area on
the inner surface of the tube allows the radiant heat
to increase and the ventilation resistance to
decrease.
The
refrigerant line connection has a bolt at the
block joint, for easy servicing.
RECEIVER/DRIER
The receiver/drier performs four functions;
• As the quantity of refrigerant circulated varies
depending on the refrigeration cycle conditions,
sufficient refrigerant is stored for the refrigera­
tion cycle to operate smoothly in accordance
with fluctuations in the quantity circulated. •
The liquefied refrigerant from the condenser
is
mixed with refrigerant gas containing air bub­
bles. If refrigerant containing air bubbles is sent
to the expansion valve, the cooling capacity will
decrease considerably. Therefore, the liquid
and air bubbles are separated and only the
liquid is sent to the expansion valve.
•
The receiver/drier utilizes a filter and dryer to
remove the dirt and water mixed in the cycling
refrigerant.
• The sight glass, installed atop the receiver/
drier, show the state of the refrigerant.
A receiver/drier may fail due to a restriction inside
the body of the unit. A restriction at inlet to the re­
ceiver/drier
will cause high pressures.
Outlet restrictions will be indicated by low pressure
and
little or no cooling. An excessively cold re­
ceiver/drier
outlet may indicate a restriction.
The receiver/drier
of this vehicle is made of alu­
minum with a smaller tank. It has 300 cc refrigerant
capacity.
The
refrigerant line connection has a bolt at the
block joint, for easy servicing.
PRESSURE SWITCH
The pressure switch (Dual pressure switch) is in­
stalled on the upper part of the receiver/drier, to
detect excessively high pressure (high pressure
switch) and prevent compressor seizure due to the
refrigerant leaking (low pressure switch), so that the
compressor is able to turned "ON" or "OFF".
The pressure characteristics of HFC-134a refrigerant
differ from those of R-12. Thus, the pressure switch
operation for HFC-134a systems has been changed
from R-12.
• Compressor ON · OFF (kPa/psi)
Low-pressure control
ON: 186.3 ± 29.4 (27.0 ± 4.3)
OFF: 176.5 ± 19.6 (25.6 ± 2.8)
High-pressure
control
ON: 2059.4 ± 196.1 (341.3 ± 28.4)
OFF: 2942.0 ± 196.1 (426.6 ± 28.4)

Fig. 18-3
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 tempera­
ture sensor, diaphragm, ball valve, ball seat, spring
adjustment 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 diaphragm.
The refrigerant pressure is transmitted to the dia­
phragms bottom chamber through the external
equalizing
pressure tube.
The
ball valve is connected to the diaphragm. The
opening 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
refrigerant. Accordingly, when a malfunction occurs
to this expansion valve, both discharge and suction
pressures
get low, resulting in insufficient cooling
capacity of the evaporator.
The
calibration has been changed to match the
characteristics of HFC-134a.
AIR CONDITIONING 1 B - 5
Fig. 18-4
EVAPORATOR
The evaporator cools and dehumidifies the air
before the air enters the vehicle. High-pressure
liquid refrigerant flows through the expansion valve
into the low-pressure 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 outside 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 cause
is
typically a partially plugged core due to dirt, or a
malfunctioning blower motor.
The evaporator core with a laminate louver fin is a
single-sided tank type where only one tank is
provided under the core.
Evaporator core
=
Fig. 18-5