Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 28

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).

<Mode switch operation>
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.

<Defroster switch operation>
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
“Self-Diagnosis Function” 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 “Checking Procedures by Failed
Location”.  As for a location this function is unappreciable,
the system accurately determines characteristics of a
given trouble and checks relevant parts according to the
“Checking Procedures by Failed Location”.
The following illustrates basic troubleshooting flow.

Basic Troubleshooting Flow

F01RX009