ISUZU AXIOM 2002 Service Repair Manual

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
1A±75
A
/
C
´
S
w
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t
c
hWhen the A/C switch is pressed, the LED light goes out and the
compressor turns off. If the switch is pressed again, the LED light
turns on and the compressor begins to operate.
The air conditioner will not operate if the fan switch is off.
During manual DEF or D/F operation, the A/C LED will turn on or off
in response to switch operation. However, the compressor remains
on regardless of switch position.
D
E
F

M
o
d
e

S
w
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t
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hWhen the defrost switch (DEF) is pressed, air flows from the de-
froster outlets. The compressor is on and blower speed is automati-
cally controlled. Air intake is from outside the vehicle (FRESH). The
defroster symbol appears on the display.
When the defrost switch (DEF) is pressed again, the unit returns to
the settings in use before the defroster was turned on.

1A±76
HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
I
Pressing the intake switch permits manual control of air intake and/
or recirculation.
I
n
t
a
k
e

S
w
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c
h
If the intake switch is pressed during manual DEF or D/F, the intake
switch LED briefly turns on. However, outside air intake (FRESH)
continues.
T
e
m
p
e
r
a
t
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e

C
o
n
t
r
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hThe display panel temperature setting can be set from 18
C (65
F)
to 32
C (90
F).
Pressing and immediately releasing the  switch increases the
temperature setting in -17
C (1
F) increments. If the switch is
pressed and held, the temperature setting increases rapidly.
Pressing and immediately releasing the
switch decreases the
temperature setting in -17
C (1
F) decrements. If the switch is
pressed and held, the temperature setting decreases rapidly.
When the temperature setting is at 32
C (90
F), the unit is set to
maximum heat mode.
When the temperature setting is at 18
C (65
F), the unit is set to
maximum cooling mode.

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
1A±77
Overview of Construction, Movement
and Control of Major Parts of
Automatic Air Conditioner System
Automatic Air Conditioner Control Unit
Equipped with the built-in micro-computer, this control
unit operates on signals from sensors and input signals
from switches to offer total control of the blower fan, and
actuators used for the mode door, intake door and air mix
door.
Its self-diagnosis function enables quicker access to a
failed part and its more accurate troubleshooting.
In Car Sensor
It is a sensor used for detecting room temperature of a
vehicle. This sensor converts a given room temperature
into a resistance value before entering the data to the
automatic air conditioner control unit.
This in car sensor unites the power driven aspirator and
the motor fan so that a small amount of room air may be
constantly fed to the sensor.
This sensor is provided on the right side of meter cluster.
865R200001
Legend
(1) Meter Cluster
(2) In Car Sensor
Ambient Sensor
This sensor is used for detecting temperature outside the
vehicle. It converts a given outside air temperature into a
resistance value before entering the data to the automatic
air conditioner control unit.
Thermal effects from the condenser and radiator during
idling after a run can be measured and offset the
automatic amplifier.
This sensor is provided on the side plate situated at upper
right side of the condenser.
875R200017
Legend
(1) Ambient Sensor
(2) Condenser Assembly
Duct Sensor
The duct sensor is the sensor to detect temperature
change of the side of evaporator blower coming by fresh
recirculation of intake door or ªonº ªoffº of compressor.
The temperature is converted to resistant rate.
And it works as thermostat to control to prevent freezing
of evaporator.
This sensor is installed in the upper case of evaporator.
874R200001
Legend
(1) Sensor Part
(2) Duct Sensor Assembly
(3) Evaporator Assembly

1A±78
HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
Sun Sensor
It is a photodiode used for detecting quantity of solar
radiation. This sensor converts the offset signal
generated by changes in the interior temperature (which
results from fluctuations in solar radiation) into
photoelectric current to enter into the automatic air
conditioner control unit.
This sensor is provided at top of the center cluster upper.
865R200002
Legend
(1) Sun Sensor
(2) Center Cluster Upper
Power Transistor
Receiving base current from the automatic air conditioner
control unit, the power transistor implements stage-less
speed change of the blower fan motor. This transistor is
provided on the evaporator.
874R200009
Legend
(1) Evaporator Assembly
(2) Power Transistor
Max Hi Relay
This relay turned on or off by the signal from the automatic
air conditioner control unit. As the Max Hi relay is turned
on, supply voltage is directly fed to the blower fan motor to
select the Max Hi mode.
873RY00005
Legend
(1) Blower Unit
(2) Max High Relay

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
1A±79
Actuator
The actuators are power driven type containing a small
motor. Receiving output current from the automatic air
conditioner control unit, actuators drive the heater and
blower unit mode doors.
Actuators consist of the mode actuator used for switching
the mode (blow port selection), the mix actuator used for
changing aperture of the air mix door, the intake actuator
used for switching the intake mode(fresh air/interior air)
actuator.
860R200004
Legend
(1) Mix Actuator
(2) Intake Actuator
(3) Blower Unit
(4) Mode Actuator
(5) Heater Unit
The actuator changes the motor speed using the gear
and drives each door rotating the output axis united with
the sliding contact.
860RW026
Legend
(1) Output Axis
(2) Motor
(3) Printed Circuit Board
(4) Sliding Contact
The mode and mix actuators are common actuators with
the built-in potentiometer. For the intake actuator, the
contact switch type is selected.
The potentiometer is a register assembled to the printed
circuit board of the mix and mode actuators. It detects the
air mix door position specified by rotation of the output
axis as a ratio of the variable terminal (VM) voltage
against the reference voltage (VDD: 5V), then signals the
value to the automatic air conditioner control unit.
C01RX016

1A±80
HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
Movement of Mix Actuator
Position of the air mix door is determined by the controller
on the automatic air conditioner control unit.
As the heat or cool side of the controller is grounded, the
transistor on the driver is activated and, thus, the motor
rotation is turned on. The sliding contact connected to the
motor sends the position detection signal from the
potentiometer to the automatic air conditioner control
unit. As the set temperature and interior temperature are
balanced, the controller returns to the neutral and the
motor rotation is stopped.
C-43
Rotation
direction
Remarks
(+) side(-) sidedirection
86ClockwiseFull heat side
68Counter
clockwiseFull cool side
C01RX005
Movement of Mode Actuator
As target position of the mode door is decided on the
controller of the control unit, the control unit reads the
position detection signal from the actuator to select the
clockwise or counter clockwise motor rotation direction.
Grounding the controller VENT or DEF side after the
direction selection activates the transistor on the driver,
thus turning on the motor rotation. Accompanying the
motor rotation, the sliding contact rotates, too. When the
target position is reached, the controller on the control
unit returns to the neutral and the motor stops.
Conduction pin
Rotation
direction
Remarks
(+) side(-) sidedirection
51ClockwiseVENT to DEF
direction
15Counter
clockwiseDEF to VENT
direction
C01RX017

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
1A±81
Movement of Intake Actuator
The controller on the automatic heater/air conditioner
control unit selects an intake mode to be used.
As the Terminal No.5 C-33 is grounded via the sliding
contact on the terminal plate, the transistor on the driver is
activated, thus turning on the motor rotation. Then,
accompanying move of the motor, the sliding contact
rotates until grounding of the Terminal No.5 C-33 is
removed, thus stopping the motor.
Grounding
terminal
Rotation
directionRemarks
No.5 C-33ClockwiseRE-CIRCULATI
ON"MIX"
FRESH
C01RX006
Overview of Automatic Control of
Automatic Air Conditioner
The automatic air conditioner on this vehicle has the
following features:

Interior temperature control.

Air flow control.

Mode (blow port) control.

Intake (switching between fresh air and interior air)
control.

Heater start timing control.

Cooler start timing control.

Evaporator anti-freeze control.

1A±82
HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
Automatic Air Conditioning System
System Overview (Chart)
Conditions both inside and outside the vehicle are
detected by sensors (in-car temperature sensor, ambient
temperature sensor, duct sensor, sun sensor, speed
sensor, and water temperature sensor). These sensors
send signals to the control unit.
Potentiometer position sensors send data to the control
unit. Signals related to control panel settings are also sent
to the control unit.In response to the signals received, the control unit
automatically adjusts air-mix door aperture (outlet air
temperature), fan speed (forced air volume), and air
intake (outside air, recirculated inside air, or a mixture of
the two).
F01R200003

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
1A±83
Interior Temperature Control
When the temperature control switch is set to a specific
temperature, a signal is sent to the A/C control unit. Other
signals are sent to the control unit from the various
sensors. This data is analyzed by the control unit which
creates a composite data signal that is compared with the
signal received from the potentiometer. The result
determines the direction of mix actuator rotation.
The mix actuator reacts to the composite air mix door
opening angle signal. Opening angle is increased or
decreased to maintain the temperature at the selected
level.
When the compressor is off, the air mix door moves
toward the COOL side. When the compressor turns on,
the temperature of the air being discharged from the
outlet vents is regulated.
When the temperature control is set to 18
C (65
F), the
air mix door moves to the FULL COOL position. When the
control is set to 32
C (90
F), the door moves to the FULL
HOT position.
In the VENT position, the air mix door moves from FULL
COOL to a 60% aperture. This prevents hot air from being
discharged into the vehicle.
C01R200005
Air Flow Control
In the Auto Mode

Automatic operation
When the AUTO switch or the DEF switch is pressed, a
signal indicating the forced air volume is sent to the A/C
auto-control unit. Other signals are sent to the control
unit from the various sensors. This data is analyzed by
the control unit which creates a composite data signal.
Based on this signal, the base voltage of the power
transistor is varied to change the blower voltage. This
results in a non-stepped change in blower motor
speed.
When the temperature control switch is set to either
18
C (65
F) or 32
C (90
F), blower motor speed is in
the MAX-HI mode.
In the Manual Mode

Manual operation
When the fan switch is manually set to a specified air
volume, a signal is sent to the A/C auto-control-unit. In
response to this signal, the auto-control unit controls
the blower voltage.
When the fan switch is set to HI, the max-hi relay
operates to increase blower motor speed to the
MAX-HI mode.
C01R200001

1A±84
HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
Mode (Blow Port) Control
The A/C control unit receives temperature setting data as
well as temperature and solar radiation level data from the
various sensors. Based on this data, the control unit
compiles a composite TMO signal. The TMO signal
allows the outlet positions to be changed in a set pattern
(VENT"BI-LEVEL"FOOT"DEFROST/FOOT).
The mode actuator acts in response to mode position. It
compares data signals received from the target mode, the
door position, and mode door position to determine the
direction of rotation.
If the temperature is set to 18
C (65
F), cool air is
discharged from the head outlets. If t he temperature is
set to 32
C (90
F), warm air is discharged from the foot
outlets.
In manual mode, existing air outlet settings remain
unchanged when the temperature is set to 18
C (65
F) or
32
C (90
F).

Press the mode switch to change to the outlet mode.
Blower operation (outlet mode position) can now be
switched between the VENT, BI-LEVEL, FOOT, and DEF
positions.

The DEF position can be selected from the outlet mode.
C01R200003
Intake (Fresh air/interior air switching)
Control
During automatic operation, the A/C control unit responds
to the temperature setting signal together with signals
from the various sensors to generate a general signal that
controls operation in a prescribed pattern.
If either or both the fan and the cooler are off, air intake is
from outside the vehicle.
If the temperature control switch is set to either 18
C
(65
F) or 32
C (90
F), the air inside the vehicle is
recirculated.
1. Manual switch operation
Press the intake switch to change between outside air
intake and recirculated inside air.
2. Defrost switch operation
Air intake is from outside the vehicle.
3. Mode switch operation
During automatic operation, outside air intake or
recirculated inside air is selected as appropriate.
During manual operation or when the DEF mode is
selected, air intake is from outside the vehicle.
C01R200004