Subaru Legacy (2005 year). Manual - part 874

AC(diag)-13

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Diagnostic Chart for Self-Diagnosis

3. A/C CONTROL SYSTEM SELF-DIAGNOSIS

Step

Check

Yes

No

1

SET SELF-DIAGNOSIS MODE BY OPERAT-
ING A/C CONTROL PANEL.
1) Turn the ignition switch to OFF.
2) Start the engine with the auto switch and 
FRESH/RECIRC switch pressed.

NOTE:

Self-diagnosis can also be performed with igni-
tion switch ON, but start the engine because
telling the magnet clutch operation is difficult.

3) All the indicator blinks four times.

Does the self-diagnosis mode 
operate?

Go to step 2.

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

2

CHECK EACH SENSOR AND POTENTIO-
METER
1) After the indicators are completed to blink, 
automatically 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 the defective sensor according to 
the sensor check table. <Ref. to AC(diag)-14, 
SENSOR CHECK TABLE, OPERATION, Diag-
nostic Chart for Self-Diagnosis.>

Are other codes except “20” 
displayed?

Repair the defec-
tive sensor. <Ref. 
to AC(diag)-30, 
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)-
14, OPERATING MODE TABLE, OPERATION, 
Diagnostic Chart for Self-Diagnosis.>

Do the actuator, blower fan and 
magnet clutch operate along 
the operating mode table?

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

Repair the mal-
function part in 
accordance with 
each diagnostic 
chart. <Ref. to 
AC(diag)-15, Diag-
nostics for A/C 
System Malfunc-
tion.> or <Ref. to 
AC(diag)-24, Diag-
nostic Procedure 
for Actuators.>

AC(diag)-14

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Diagnostic Chart for Self-Diagnosis

4. SENSOR CHECK TABLE

NOTE:
When the sunload sensor check is conducted indoors or in the shade, open circuit might be indicated. Always
check the sunload sensor at the place where the sun shines directly on it.

*1: “AUTO” display does not blink when past malfunction occurred. Past malfunction means that abnormal signal had input for a
certain time continuously in the past.
*2: Present malfunction only is displayed for sunload sensor open circuit.

5. OPERATING MODE TABLE

Display screen (Malfunction at 

present) *1

SENSOR

Trouble contents

21/AUTO Blink

In-vehicle sensor

Broken

−21/AUTO Blink

Short

22/AUTO Blink

Ambient sensor

Sensor trouble or communication malfunction

23/AUTO Blink

Evaporator sensor

Broken

−23/AUTO Blink

Short

24/AUTO Blink

Engine coolant temperature sensor

Sensor trouble or communication malfunction

25 Blink

Sunload sensor

Open *2

−25/AUTO Blink

Short

26/AUTO Blink

Air mix door actuator 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)-15

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Diagnostics for A/C System Malfunction

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:

A1

A9

A2

A16

B282

A:

B283

B:

AUTO A/C CONTROL MODULE

BATTERY

M/B No. 8

F/B No. 22

F/B No. 31

MAIN SBF

SBF-6

B282

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

B283

1 2 3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18 19 20

A:

B:

IGNITION

SWITCH

AC-01248

E

ACC

i88

1

2

5

B16

B15

3

7

A14

10

1

1

*

i97

i3

B38

JOINT
CONNECTOR

A/C CONTROL PANEL

1 2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

B38

1 2 3 4 5 6
7 8 9 10 11 12

i97

1 2 3 4
5 6 7 8

i88

*

: LHD MODEL : 4
  RHD MODEL : 6

AC(diag)-16

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Diagnostics for A/C System Malfunction

Step

Check

Yes

No

1

CHECK FUSE.
1) Turn the ignition switch to OFF.
2) Remove the fuse No. 8 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 and 31 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.
1) Replace the A/C control panel.
2) Disconnect the A/C control panel harness 
connector.
3) Measure the voltage between A/C control 
panel harness connector terminal and chassis 
ground after turning the ignition switch to ACC 
position.

Connector & terminal

(i88) No. 2 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 4.

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

4

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 
position.

Connector & terminal

(i88) No. 1 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 5.

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

5

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

Connector & terminal

(i88) No. 5 — Chassis ground:

Is the resistance less than 10 
Ω?

Go to step 6.

Repair the har-
ness for ground 
line.

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 OFF posi-
tion.

Connector & terminal

(B282) No. 1 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 7.

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

7

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 ACC posi-
tion.

Connector & terminal

(B282) No. 2 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 8.

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

8

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 ON position.

Connector & terminal

(B282) No. 9 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 9.

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