Infiniti Q45 (FY33). Manual — part 487
Blower Motor Circuit
SYSTEM DESCRIPTION
Component parts
Fan speed control system components are:
1) Auto amplifier
2) Fan control amplifier
3) A/C LAN system (PBR)
4) In-vehicle sensor
5) Ambient sensor
6) Sunload sensor
7) Intake sensor
8) Thermal transmitter
9) A/C control unit (PTC, AUTO, ECON, MODE, DEFROST, BLOWER, OFF switches)
System operation
For description of system operation, see next page.
RHA168F
Automatic mode
In the automatic mode, the blower motor speed is calculated by the automatic amplifier based on inputs from
the PBR, in-vehicle sensor, sunload sensor, and ambient sensor. The blower motor applied voltage ranges
from approximately 4 volts (lowest speed) to 12 volts (highest speed).
The control blower speed (in the range of 4 to 12V), the automatic amplifier supplies a signal to the fan con-
trol amplifier. Based on this signal, the fan control amplifier controls the current flow from the blower motor to
ground. If the computed blower voltage (from automatic amplifier) is above 10.5 volts, the high blower relay
is activated. The high blower relay provides a direct path to ground (bypassing the fan control amplifier), and
the blower motor operates at high speed.
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TROUBLE DIAGNOSES
HA-113
Starting blower speed control
Start up from “COLD SOAK” condition (Automatic mode)
In a cold start up condition where the engine coolant temperature is below 56°C (133°F) and the ambient
temperature is below 15°C (59°F), the blower will not operate for a short period of time (up to 90 seconds).
The exact start delay time varies depending on the ambient and engine coolant temperature.
In the most extreme case (very low ambient) the blower starting delay will be 150 seconds as described above.
After this delay, the blower will operate at low speed until the engine coolant temperature rises above 32°C
(90°F), at which time the blower speed will increase to the objective speed.
Start up from normal or “HOT SOAK” condition
(Automatic mode)
The blower will begin operation momentarily after the AUTO button is pushed. The blower speed will gradu-
ally rise to the objective speed over a time period of 3 seconds or less (actual time depends on the objective
blower speed).
Blower speed compensation
Sunload
When the in-vehicle temperature and the set temperature are very close, the blower will be operating at low
speed. The low speed will vary depending on the sunload. During conditions of high sunload, the blower low
speed is “normal” low speed (approx. 6V). During low or no sunload conditions, the low speed will drop to “low”
low speed (approx. 5V).
Ambient
When the ambient temperature is in the “moderate” range [10 - 15°C (50 - 59°F)], the computed blower volt-
age will be compensated (reduced) by up to 3.5V (depending on the blower speed). In the “extreme” ambi-
ent ranges [below 0°C (32°F) and above 20°C (68°F)] the computed objective blower voltage is not compen-
sated at all. In the ambient temperature ranges between “moderate” and “extreme” [0 - 10°C (32 - 50°F) and
15 - 20°C (59 - 68°F)], the amount of compensation (for a given blower speed) varies depending on the ambi-
ent temperature.
Fan speed control specification
RHA979F
TROUBLE DIAGNOSES
Blower Motor Circuit (Cont’d)
HA-114
RHA951F
COMPONENT DESCRIPTION
Fan control amplifier
The fan control amplifier is located on the cooling unit. It amplifies
the base current flowing from the auto amplifier to change the
blower speed within the range of 4V to 12V.
RHA964F
DIAGNOSTIC PROCEDURE
SYMPTOM: Blower motor operation is malfunctioning under
out of starting Fan Speed Control.
I
Perform Preliminary Check 5 before referring to the fol-
lowing flow chart.
SHA820E
RHA920F
RHA921F
CHECK POWER SUPPLY FOR AUTO
AMP.
Disconnect auto amp. harness connec-
tor.
Do approx. 12 volts exist between auto
amp. harness terminal
q
33
and body
ground?
Yes
E
No
Check power supply circuit
and 15A fuses (No.
and
, located in the fuse
block).
Refer to EL section (“Wiring
Diagram”, “POWER SUPPLY
ROUTING”).
CHECK POWER SUPPLY FOR FAN
CONTROL AMP.
Disconnect fan control amp. harness
connector.
Do approx. 12 volts exist between fan
control amp. harness terminal
q
35
and
body ground?
Yes
E
No
CHECK POWER SUPPLY
FOR BLOWER MOTOR.
Disconnect blower motor har-
ness connector.
Do approx. 12 volts exist
between blower motor har-
ness terminal
q
1
and body
ground?
Yes
No
Note
CHECK BODY GROUND CIRCUIT FOR
FAN CONTROL AMP.
Check harness continuity between fan
control amp. harness terminal
q
G
and
body ground.
Continuity should exist.
If OK, check harness for short.
OK
Check power sup-
ply circuit and 15A
fuses (No.
and
, located in the
fuse block). Refer
to EL section (“Wir-
ing Diagram”,
“POWER SUPPLY
ROUTING”).
Reconnect fan control amp. harness
connector and auto amp. harnesses con-
nector.
Note
Check circuit continuity
between blower motor har-
ness terminal
q
2
and fan con-
trol amp. harness terminal
q
35
.
Continuity should exist.
If OK, check harness for
short.
OK
q
A
(Go to next page.)
q
B
(Go to next page.)
Note:
If the result is NG or No after checking circuit continuity, repair harness
or connector.
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IDX
TROUBLE DIAGNOSES
Blower Motor Circuit (Cont’d)
H
H
H
H
H
H
H
HA-115
RHA922FA
RHA549FB
RHA923F
RHA181H
RHA182H
q
A
q
B
CHECK VOLTAGE FOR FAN CONTROL
AMP.
Set up Self-diagnosis STEP 4.
Measure voltage across fan control amp.
harness terminal
q
34
and body ground.
CHECK BLOWER MOTOR.
(Refer to Electrical Compo-
nents Inspection.) (HA-
HA-117)
NG
OK
Replace blower motor.
H
NG
(Less than 2.5V)
E
NG
(More than 3.0V)
CHECK FAN CONTROL
AMP.
(Refer to “Electrical Compo-
nents Inspection”.) (HA-117)
NG
OK
Replace fan control amp.
F
H
Disconnect auto amp. and fan control
amp. harness connector.
Yes
Note
Check circuit continuity between auto amp.
harness terminal No.
q
35
and fan control
amp. harness terminal No.
q
34
.
Continuity should exist.
If OK, check harness for short.
OK
Note
Check circuit continuity between auto amp.
harness terminal No.
q
34
and fan control
amp harness terminal No.
q
35
.
Continuity should exist.
If OK, check harness for short.
OK
q
C
(Go to next page.)
Note:
If the result is NG or No after checking circuit continuity, repair harness
or connector.
Code No.
Terminal No.
Voltage
!
@
q
34
Body
ground
Approx.
2.5 - 3.0V
TROUBLE DIAGNOSES
Blower Motor Circuit (Cont’d)
H
H
H
H
H
H
H
HA-116
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