Subaru Legacy IV (2008 year). Manual - part 990

AC(diag)-12

Diagnostic Chart for Self-Diagnosis

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

3. A/C CONTROL SYSTEM SELF-DIAGNOSIS

Step

Check

Yes

No

1

SET SELF-DIAGNOSIS MODE BY OPERAT-
ING A/C CONTROL PANEL.
1) Start the engine with the A/C switch and 
front defroster switch pressed.

NOTE:
Self-diagnosis can also be performed with igni-
tion switch ON, but start the engine because ob-
serving the magnet clutch operation is difficult.
2) All the indicators blink four times.

Does the self-diagnosis func-
tion operate?

Go to step 2.

<Ref. to AC(diag)-
14, A/C OR SELF-
DIAGNOSIS SYS-
TEMS DO NOT 
OPERATE, Diag-
nostics for A/C 
System Malfunc-
tion.>

2

CHECK EACH SENSOR AND POTENTIOME-
TER.
1) After the indicators stop blinking, automati-
cally change to the Inspection Mode of sensor 
and potentiometer.

NOTE:
Display items can be changed each time the A/
C switch is pressed. (Step Operation)
2) When malfunction occurs in each sensor 
and potentiometer, codes are displayed on the 
screen. When no malfunction occurs in each 
sensor and potentiometer, code “20” is dis-
played on the screen.
3) Identify defective sensors according to the 
sensor check table. <Ref. to AC(diag)-13, SEN-
SOR CHECK TABLE, OPERATION, Diagnostic 
Chart for Self-Diagnosis.>

Are other codes except “20” 
displayed?

Repair the defec-
tive sensor. <Ref. 
to AC(diag)-29, 
Diagnostic Proce-
dure for Sensors.>

Go to step 3.

3

CHECK EACH ACTUATOR, BLOWER FAN 
AND MAGNET CLUTCH.
1) After completing each sensor and potenti-
ometer inspection, change to the Inspection 
Mode of actuator, blower fan and magnet clutch 
by pressing the defroster switch.
2) Each mode will change and operate auto-
matically every four seconds.

NOTE:
Operation mode items can be changed each
time the A/C switch is pressed. (Step Opera-
tion)
3) Check the operation of actuator, blower fan 
and magnet clutch in each mode according to 
the operating mode table. <Ref. to AC(diag)-13, 
OPERATING MODE TABLE, OPERATION, 
Diagnostic Chart for Self-Diagnosis.>

Do the actuator, blower fan and 
magnet clutch operate as 
described in the operating 
mode table?

A/C control system 
is normal. Press 
the OFF switch 
and complete the 
self-diagnosis 
function.

Repair the defec-
tive part in accor-
dance with each 
diagnostic chart. 
<Ref. to AC(diag)-
14, Diagnostics for 
A/C System Mal-
function.> or <Ref. 
to AC(diag)-22, 
Diagnostic Proce-
dure for Actua-
tors.>

AC(diag)-13

Diagnostic Chart for Self-Diagnosis

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

4. SENSOR CHECK TABLE

NOTE:
When the sunload sensor check is performed indoors or in the shade, it could be diagnosed as having an
open circuit. Always check the sunload sensor with the sun shining on it.

*1: AUTO display does not blink when past malfunction occurred. Past malfunction means that abnormal signals were continu-
ously input for a certain time in the past.
*2: Present malfunction only is displayed for sunload sensor open circuit.

5. OPERATING MODE TABLE

* Same opening angle for both driver’s and passenger’s side

Display screen (Malfunction at 

present) *1

Sensor

Trouble contents

21/AUTO Blink

In-vehicle sensor

Open

–21/AUTO Blink

Short

22/AUTO Blink

Ambient sensor

Sensor trouble or communication failure

23/AUTO Blink

Evaporator sensor

Open

–23/AUTO Blink

Short

24/AUTO Blink

Engine coolant temperature sensor

Sensor trouble or communication failure

25 Blink

Sunload sensor

Open *2

–25/AUTO Blink

Short

26/AUTO Blink

Driver’s side air mix door actuator 

potentiometer

COOL

27/AUTO Blink

HOT

–26/AUTO Blink

Passenger’s side air mix door actua-

tor potentiometer

COOL

–27/AUTO Blink

HOT

28/AUTO Blink

Mode door actuator potentiometer

FACE

29/AUTO Blink

DEF

20 Blink

When all conditions are normal

Display screen

FRESH/RECIRC

door

Mode door

Air mix door*

Blower fan

A/C compressor (Mag-

net clutch)

31

FRESH

FACE

Maximum cool

LO

OFF

32

RECIRC

FACE

Maximum cool

LO

ON

33

RECIRC

FACE

Maximum cool

M1

ON

34

FRESH

B/L

50%

M1

ON

35

FRESH

FOOT

50%

M1

ON

36

FRESH

FOOT

Maximum hot

M3

ON

37

FRESH

F/D

Maximum hot

M3

ON

38

FRESH

DEF

Maximum hot

HI

ON

AC(diag)-14

Diagnostics for A/C System Malfunction

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

6. Diagnostics for A/C System Malfunction

A: A/C OR SELF-DIAGNOSIS SYSTEMS DO NOT OPERATE

TROUBLE SYMPTOM:
• Set temperature is not indicated on the display, switch LEDs are faulty and switches do not operate.
• Self-diagnosis system does not operate.
WIRING DIAGRAM:

1

21

28

B282

M/B No. 7

F/B No. 22

MAIN SBF

SBF-6

B282

E

i88

1

5

35

34

3

7

10

1

i3

B38

B38

i88

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

1 2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

1 2 3 4
5 6 7 8

AC-01682

AUTO A/C CONTROL MODULE

A/C CONTROL PANEL

IGNITION
SWITCH

BATTERY

AC(diag)-15

Diagnostics for A/C System Malfunction

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK FUSE.
1) Turn the ignition switch to OFF.
2) Remove the fuse No. 7 from main fuse box.
3) Check the condition of fuse.

Is the fuse blown out?

Replace the fuse.

Go to step 2.

2

CHECK FUSE.
1) Turn the ignition switch to OFF.
2) Remove the fuse No. 22 from fuse & relay 
box.
3) Check the condition of fuse.

Is the fuse blown out?

Replace the fuse.

Go to step 3.

3

CHECK A/C CONTROL PANEL POWER CIR-
CUIT.
Measure the voltage between A/C control panel 
harness connector terminal and chassis ground 
after turning the ignition switch to ON.

Connector & terminal

(i88) No. 1 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 4.

Check for open or 
short circuit in the 
harness between 
A/C control panel 
and fuse.

4

CHECK A/C CONTROL PANEL GROUND 
POWER CIRCUIT.
Measure the resistance of harness between A/
C control panel and chassis ground after turn-
ing the ignition switch to OFF.

Connector & terminal

(i88) No. 5 — Chassis ground:

Is the resistance less than 10 

:? Go to step 5.

Repair the harness 
for ground line.

5

CHECK AUTO A/C CONTROL MODULE 
POWER CIRCUIT.
Measure the voltage between auto A/C control 
module connector terminal and chassis ground 
after turning the ignition switch to OFF.

Connector & terminal

(B282) No. 1 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 6.

Check open or 
short circuit of har-
ness between auto 
A/C control module 
and fuse.

6

CHECK AUTO A/C CONTROL MODULE 
POWER CIRCUIT.
Measure the voltage between auto A/C control 
module connector terminal and chassis ground 
after turning the ignition switch to the ON posi-
tion.

Connector & terminal

(B282) No. 21 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 7.

Check open or 
short circuit of har-
ness between auto 
A/C control module 
and fuse.

7

CHECK AUTO A/C CONTROL MODULE 
GROUND CIRCUIT.
Measure the resistance of harness between 
auto A/C control module and chassis ground.

Connector & terminal

(B282) No. 28 — Chassis ground:

Is the resistance less than 5 

:? Go to step 8.

Repair the harness 
for ground line.

8

CHECK COMMUNICATION CIRCUIT.
Measure the resistance of harness between A/
C control panel and auto A/C control module.

Connector & terminal

(i88) No. 3 — (B282) No. 35:
(i88) No. 7 — (B282) No. 34:

Is the resistance less than 1 

:? Go to step 9.

Repair the har-
ness.

9

CHECK POOR CONTACT.
Check poor contact of auto A/C control module 
connector.

Is there poor contact in connec-
tor?

Repair the connec-
tor.

Replace the auto 
A/C control mod-
ule.