Subaru Legacy III (2000-2003 year). Service manual — part 878

AC-48

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

DIAGNOSTICS FOR A/C SYSTEM FAILURE (RHD MODEL)

12

CHECK GROUND CIRCUIT OF SUB FAN
MOTOR.
1) Turn ignition switch to OFF.
2) Measure resistance between sub fan motor

connector and chassis ground.

Connector & terminal

4 CYLINDER MODEL

(F16) No. 1 — Chassis ground:

6 CYLINDER MODEL

(F16) No. 4 — Chassis ground:

Is the measured value less than the speci-
fied value?

1

Ω

Go to step 13.

Repair harness
between sub fan
motor connector
and chassis
ground.

13

CHECK POOR CONTACT.
Check poor contact in sub fan motor connec-
tor.
Is there poor contact in connector?

There is no poor contact in
connector.

Go to step 14.

Repair poor con-
tact in sub fan
motor connector.

14

CHECK SUB FAN MOTOR.
4 CYLINDER MODEL
Connect battery positive (+) terminal to termi-
nal No. 2, and negative (

−

) terminal to terminal

No. 1 of sub fan motor connector.
6 CYLINDER MODEL
Connect battery positive (+) terminal to termi-
nal No. 1, 2, 3, and negative (

−

) terminal to ter-

minal No. 4 of sub fan motor connector.
Does the sub fan motor rotate?

Sub fan motor rotates.

Go to step 15.

Replace sub fan
motor with a new
one.

15

CHECK EACH SENSOR AND POTENTIOME-
TER.
Check the sensors and potentiometer for
proper operation using the self-diagnostic
function. <Ref. to AC-18, OPERATION, Self-
Diagnosis Procedure (RHD Model).>
Is the operation of each sensor and potentiom-
eter normal?

Operation of each sensor and
potentiometer is OK.

Go to step 16.

Replace sensor
and/or potentiome-
ter.

16

CHECK CONNECTION OF ASPIRATOR
DUCT.
Make sure that the connection of aspirator duct
is correct.
Is the connection of duct correct?

Connection is OK.

Go to step 17.

Repair aspirator
duct connection.

17

CHECK EACH ACTUATOR.
Check the actuators for proper operation using
the self-diagnostic function. <Ref. to AC-18,
OPERATION, Self-Diagnosis Procedure (RHD
Model).>
Is the operation of each actuator normal?

Operation of each actuator is
OK.

Go to step 18.

Replace actuator.

18

CHECK POOR CONTACT.
Check poor contact in A/C control module con-
nector.
Is there poor contact in connector?

There is no poor contact.

Replace A/C con-
trol module.

Repair connector.

Step

Value

Yes

No

AC-49

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

LIST OF DIAGNOSTIC TROUBLE CODE (DTC)

9. List of Diagnostic Trouble Code (DTC)

A: LIST (LHD MODEL)

1. DTC FOR SENSOR AND POTENTIOMETER

2. DTC FOR MODE DOOR POSITION SWITCH

B: LIST (RHD MODEL)

1. DTC FOR SENSOR AND POTENTIOMETER

DTC

Trouble Unit

Contents

20

No Trouble

—

21

Ambient sensor

Open

–21

Short

22

In-vehicle sensor

Open

–22

Short

24

Evaporator sensor

Open

–24

Short

25

Sunload sensor

Open

–25

Short

26

Mode door actuator

Open

–26

Short

DTC

30

31

32

33

34

35

Faulty Door

No Trouble

VENT

B/L

HEAT

D/H

DEF

DTC

Trouble Unit

Contents

20

No Trouble

—

21

In-vehicle sensor

Open

–21

Short

22

Ambient sensor

Open

–22

Short

23

Evaporator sensor

Open

–23

Short

25

Sunload sensor

Open

–25

Short

26

Air mix door actuator

FULL COOL

27

FULL HOT

28

Mode door actuator

FULL VENT

29

FULL DEF

AC-50

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC) (LHD

MODEL)

10.Diagnostic Procedure with Diagnostic Trouble Code (DTC) (LHD

Model)

A: DTC 21 OR –21 (AMBIENT SENSOR)

TROUBLE SYMPTOM:
Fan speed, outlets and inlets are not switched when AUTO or ECON switch is ON.
WIRING DIAGRAM:

AC-00371

B17

B6

F78

F2

B100

B36

i1

2

1

AMBIENT

SENSOR

9

8

E6

D6

F78

1 2

i49

B:

1 2 3 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18 19 20

B36

B4 B5 B6

A4 A5 A6

C5 C6

F6

D4 D5 D6

F1

H1

C4

G6

G1

C2

K1

M1 M2

K6

L1

D1 D2

A1 A2
B1 B2

I6

J6

L2

I1

J1

H6

M4 M5 M6

L4 L5 L6

N5 N6

O4 O5 O6

N4

P4 P5

N2

O1 O2

P1 P2

N3

O3

P3

P6

A3

B3

C3

E4 E5 E6

E1 E2

i49

B:

i48

A:

AUTO A/C

CONTROL MODULE

F2

1

12

9

8

7

6

17

5

4

3

2

14

13

15 16

18

21

20

19

22 23 24

11

10

AC-51

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC) (LHD

MODEL)

Step

Value

Yes

No

1

CHECK AMBIENT SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from ambient sensor.
3) Measure resistance between connector ter-

minals of ambient sensor.

Terminals

No. 1 — No. 2:

Is the measured value the same as speci-
fied value?

Approx. 2.2 k

Ω

: 25

°

C (77

°

F)

Go to step 2.

Replace ambient
sensor.

2

CHECK INPUT SIGNALS FOR AMBIENT
SENSOR.
1) Turn ignition ON.
2) Measure voltage between ambient sensor

harness connector terminals.

Connector & terminal

(F78) No. 1 (+) — No. 2 (

−−−−

):

Is the measured value the same as speci-
fied value?

Approx. 4.5 V

Go to step 6.

Go to step 3.

3

CHECK OUTPUT SIGNALS FROM A/C CON-
TROL MODULE.
1) Turn ignition switch to OFF.
2) Pull out A/C control panel.
3) Disconnect connector from ambient sensor.
4) Turn ignition switch to ON.
5) Measure voltage between connector termi-

nals of A/C control module.

Connector & terminal

(i49) No. 6 (+)— No. 17 (

−−−−

):

Is the measured value the same as speci-
fied value?

Approx. 4.5 V

Go to step 4.

Go to step 6.

4

CHECK HARNESS CONNECTOR BETWEEN
A/C CONTROL MODULE AND AMBIENT
SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connectors from A/C control

module.

3) Measure resistance of harness between A/

C control module and ambient sensor.

Connector & terminal

(F78) No. 1 — (i49) No. 6:

Is the measured value less than the speci-
fied value?

1

Ω

Go to step 5.

Repair harness
between A/C con-
trol module and
ambient sensor.

5

CHECK HARNESS CONNECTOR BETWEEN
A/C CONTROL MODULE AND AMBIENT
SENSOR.
Measure resistance of harness between A/C
control module and ambient sensor.

Connector & terminal

(F78) No. 2 — (i49) No. 17:

Is the measured value less than the specified
value?

1

Ω

Go to step 6.

Repair harness
between A/C con-
trol module and
ambient sensor.

6

CHECK POOR CONTACT.
Check poor contact in A/C control module con-
nector.
Is there poor contact in connector?

There is no poor contact.

Replace A/C con-
trol module.

Repair connector.