2002 ISUZU AXIOM Service Repair Manual

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

HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
1A±85
Compressor Control
In the automatic control mode, the automatic air
conditioner control unit turns on or off the compressor
with the evaporator anti-freeze mechanism using the
evaporation sensor. And, when outside air is detected to
be low through the outside air temperature sensor signal,
the control unit turns off the compressor using the
compressor control function.
Manual Control

In the automatic control mode, pressing the A/C (air
conditioning) switch turns off the compressor.

Pressing the DEF mode switch automatically turns on
the compressor.
C01R200002
Heater Start-up Control
Heater start-up control occurs when the air discharge
mode is in the BI=LEVEL, FOOT, or DEF/FOOT position
and the heater core temperature is less than 14
C (58
F).
Air discharge volume remains in the AUTO LO mode until
the engine coolant temperature rises above 14
C (58
F).
The volume then increases in linear increments to the
pre-set level.
840R200010
Cooler Start-up Control
When cooler operation is started with the air discharge
mode is in the VENT or B/L position and the in-car
temperature higher than 26
C (78
F) (detected by the
in-car sensor), cooler start-up control occurs.
For the first 7 seconds of cooler operation, the fan
remains OFF. It then switches to AUTO LO. Air discharge
volume then increases in linear increments to the pre-set
level.
Cooler start-up control occurs the first time the engine is
started or the cooler switch is moved from OFF to AUTO.
It will not occur during subsequent switch movements.
C06R200001

1A±86
HEATING, VENTILATION AND AIR CONDITIONING (HVAC)
Troubleshooting
Troubleshooting, Its Overview and
Procedures
The automatic air conditioner equips with the
ªSelf-Diagnosis Functionº to check its major components.
This function makes access to the sensors, actuators and
blower fan motor system easier when checking them up
and, when a failed part is located, this function restores its
original performance.When implementing the troubleshooting, this
self-diagnosis function narrows the range to be searched
at the first step, then check relevant parts one by one
according to the ªChecking Procedures by Failed
Locationº. As for a location this function is unappreciable,
the system accurately determines characteristics of a
given trouble and checks relevant parts according to the
ªChecking Procedures by Failed Locationº.
The following illustrates basic troubleshooting flow.
Basic Troubleshooting Flow
F01RX009