Page 1937 of 2267

system operation. On the other hand, shortly after entering a
long tunnel, the system will recognize the change in sunload, and
the system will react accordingly.
SUNLOAD COMPENSATION
The auto amplifier compensates for sunload by altering the air
mix door position and air flow volume according to the amount
of sunload detected by the sunload sensor. When the amount of
sunload is great, the air mix door is moved toward the ªCOLDº
side. Along with this air mix door movement, air flow volume will
also be changed.
YHA296 A/C control panel PTC
In-vehicle sensor
Ambient sensor
Sunload sensorSunload com-
pensation Auto amplifier
Air mix door posi-
tion arithmetic cir-
cuit
Air flow volume
arithmetic circuitAir mix door motor
LOW, MED, HIGH
and AUTO relays
SHA493CA
Air mix door position
compensation amount
Sunload kW (kcal/h, BTU/h)/m2
[kW (kcal/h,BTU/h)/sq ft]
Sunload compensation specifications0.768 (660, 2,619)
[0.0713 (61.31, 243.3)]
SYSTEM DESCRIPTIONAUTO
Control System Auto Amplifier (Auto amp.)
(Cont'd)
HA-88
Page 1938 of 2267
A/C SWITCH COMPENSATION
The auto amplifier alters the air mix door position and air flow volume according to a signal emitted from the
A/C switch.
When the A/C switch is ªONº, the auto amplifier compensates for the PBR's input signal and moves the air
mix door toward the ªHOTº side.
YHA297 A/C control panel PTC
In-vehicle sensor
Ambient sensor
Sunload sensor
Sunload compensation Auto amplifier
Air mix door position arith-
metic circuit
Output signal pro-
cessAir mix door
motor
PBR
A/C control panel
A/C switch
KHA115
Air mix door opening ratio
(%)
100
15
0
Air mix door position arithmetic value
A/C switchcompensation specifications 0 100 (%)
SYSTEM DESCRIPTIONAUTO
Control System Auto Amplifier (Auto amp.)
(Cont'd)
HA-89
Page 1939 of 2267

Control System Output Components
AIR MIX DOOR CONTROL (Automatic temperature control)
Component parts
Air mix door control system components are:
1) Auto amplifier
2) Ambient sensor
3) In-vehicle sensor
4) Sunload sensor
5) Air mix door motor (PBR)
6) A/C switch
System operation
The air mix door is automatically controlled so that in-vehicle temperature is maintained to the set tempera-
ture. The temperature set by the PTC (Potentio Temperature Control) and the temperature detected by the
in-vehicle sensor and ambient sensor are compensated by the sunload sensor signal. The auto amplifier then
determines the air mix door position. The air mix door position detected by the PBR is compensated by the
ON-OFF operation of the A/C switch. The air mix door position determined by the auto amplifier is compared
with that detected by the PBR. The auto amplifier then transmits the signal to the air mix door motor in order
to activate it.
KHA116 Auto amplifier
PTC
In-vehicle sensor
Ambient
sensor
sunload
sensor
PBR
A/C switchConstant voltage
transformation
Air mix door posi-
tion arithmetic cir-
cuit
Sunload compen-
sation
Air mix door posi-
tion detection
A/C switch com-
pensationAir mix
door motor
SYSTEM DESCRIPTIONAUTO
HA-90
Page 1940 of 2267

Air mix door control specifications
SENSOR INPUT PROCESS
The auto amplifier detects the voltage produced by each sensor,
the PBR and fixed resistor. The fixed resistor is built into the auto
amplifier. 12-volt power voltage is first converted to approxi-
mately 5 volts by the constant voltage circuit where it is then
applied to the ground line of the auto amplifier via the fixed
resistor and the sensor. In this manner, the auto amplifier moni-
tors the voltages of the fixed resistor, each sensor and the PBR
to determine sensor input.
SHA497CB A/C switch OFF
A/C switch ON
Voltage (V)
ConditionPTC: 25ÉC (77ÉF)
Fan switch Auto
Withoutsunload
Ambient
temperature ÉC (ÉF)
Air mix door opening angle In vehicle temperature ÉC (ÉF)
0.5 1.0 1.5 2.0 2.5 3.0
PBRresistance (kW)2.4
2.3
2.2
2.1
2.0
1.9
(59) (68) (77) (86) (95) (104)-20 (-4)
-10 (-4)
0 (32)
10(50)
20 (68)
25 (77)
30(86)
40 (104)
54.5
RHA790A Auto amplifier
Constant-voltage
circuit
Fixed resistor
Detection of sen-
sor voltage
Each sensor
SYSTEM DESCRIPTIONAUTO
Control System Output Components (Cont'd)
HA-91
Page 1941 of 2267

OPERATION OF AIR MIX DOOR MOTOR
lExamplep1
When the temperature in the vehicle is lower than the set
temperature.
When the temperature in the vehicle is low, in-vehicle sen-
sor resistance is great and the input voltage to the auto
amplifier becomes great. As a result, the voltage from the air
mix door position arithmetic circuit also becomes great.
When this voltage is greater than the voltage from the PBR,
comparator (1), Tr
p1and Trp4turn ON.
Accordingly terminal No.
p12becomes!and terminal No.
p13becomes@. The air mix door motor rotates clockwise and
the air mix door moves toward the ªHOTº side.
As the air mix door moves toward the ªHOTº side, the volt-
age from the PBR becomes greater and consequently
becomes equal to that from the air mix door position arith-
metic circuit. As a result, comparator (1) turns OFF and the
air mix door motor stops.
RHA514DB Auto amp.
Comparator
(1)
Air mix door
position arith-
metic circuitAir mix
door
motor
PBR
Comparator
(2)
SHA568CB Auto amp.
Comparator
(1)
Air mix door
position
arithmetic
circuit
PBR
Comparator
(2)Air mix
door
motor
SYSTEM DESCRIPTIONAUTO
Control System Output Components (Cont'd)
HA-92
Page 1942 of 2267

lExamplep2
When the temperature in the vehicle is higher than the set
temperature.
When the temperature in the vehicle is high, in-vehicle sen-
sor resistance is small and the input voltage to the auto
amplifier becomes small. As a result, the voltage from the air
mix door position arithmetic circuit also becomes small.
When this voltage is smaller than the voltage from the PBR,
comparator (2), Tr
p2and Trp3turn ON.
Accordingly terminal No.
p13becomes!and terminal No.
p12becomes@. The air mix door motor rotates counterclock-
wise and the air mix door moves toward the ªCOLDº side.
As the air mix door moves toward the ªCOLDº side, the volt-
age from the PBR becomes smaller and consequently
becomes equal to that from the air mix door position arith-
metic circuit. As a result, comparator (2) turns OFF and the
air mix door motor stops.
AIR MIX DOOR MOTOR
The air mix door motor is attached to the heater unit. It rotates
so that the air mix door is opened to a position set by the auto
amplifier. Motor rotation is conveyed through a shaft. The air mix
door position is then fed back to the auto amplifier by the PBR
built into the air mix door motor.
SHA569CB Auto amp.
Comparator
(1)
Air mix door
position
arithmetic
circuit
PBR
Comparator
(2)Air mix
door
motor
SHA570CB Auto amp.
Comparator
(1)
Air mix door
position
arithmetic
circuit
PBR
Comparator
(2)Air mix
door
motor
KHA127 Air mix door link
Air mix door lever
Air mix door motor Heater unit
SYSTEM DESCRIPTIONAUTO
Control System Output Components (Cont'd)
HA-93
Page 1943 of 2267
21Air mix door
operationDirection of lever movement
!@COLD,HOTClockwise
(Toward passenger compartment)
Ð Ð STOPSTOP
@
!HOT,COLDCounterclockwise
(Toward engine compartment)
PBR
Measure voltage between terminalsp3andp4at vehicle har-
ness side.
Ignition switch: ON
lEnsure tester pointer deflects smoothly when PTC is moved
from 18ÉC (64ÉF) to 32ÉC (90ÉF) and vice versa.
RHA026H Air mix door motor
connector
M413
(HOT
side)(Cold
side)
PBR
KHA129 Characteristic PBR
Resistance of PBR (W)
(resistance between terminal
p4and
p3)
.3.0
2.5
2.0
1.5
1.0
0.5
COLD Air mix door opening angle HOT60É
NHA311 Air mix door motor
RHA607AA
Voltage (V)
Full cold Full hot
Air mix door opening angle PBR
specification5.0
4.0
3.0
2.0
1.0
0
SYSTEM DESCRIPTIONAUTO
Control System Output Components (Cont'd)
HA-94
Page 1944 of 2267

FAN SPEED CONTROL
Component parts
Fan speed control system components are:
1) Auto amplifier
2) In-vehicle sensor
3) Ambient sensor
4) Sunload sensor
5) A/C switch relay
6) A/C switch
7) Fan switch
8) Blower motor
9) Resistance
10) HI, MH, ML and LO relays
System operation
Blower fan speed is automatically controlled so that the in-vehicle temperature is maintained to the set tem-
perature.
The temperature set by the PTC (Potentio Temperature Control) and the temperature detected by the in-
vehicle sensor and ambient sensor are compensated by the sunload sensor signal. The auto amplifier then
determines fan speed from the ON-OFF operation of the A/C switch. The fan speed decision by the auto
amplifier activates the fan relay and the blower fan motor rotates. When the A/C switch is ON, fan speed is
activated in 4 steps, HI, MH, ML, and LO. When the A/C switch is OFF, fan speed is activated in 3 steps,
MH, ML, and LO.
KHA130 Auto amplifier
In-vehicle
sensor
Ambient
sensor
Sunload
sensor
A/C switchConstant voltage
transformation
Air mix door posi-
tion arithmetic cir-
cuit
Sunload compen-
sationA/C operation
signal detection
Air flow volume
arithmetic circuitHI relay
MH
relay
ML
relayBlower
motor
Resistor
LO relay
Fan switch
(AUTO)
SYSTEM DESCRIPTIONAUTO
Control System Output Components (Cont'd)
HA-95