Subaru Legacy (2005 year). Manual - part 876

AC(diag)-21

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. 22 from fuse & relay 
box.
3) Check the condition of fuse.

Is the fuse blown-out?

Replace the fuse.

Go to step 2.

2

CHECK SIGNAL TO A/C RELAY AND A/C 
CONTROL MODULE.
1) Disconnect the A/C relay and auto A/C con-
trol module harness connector.
2) Turn the ignition switch to ON.
3) Measure the voltage between A/C relay 
connector terminal and chassis ground.
4) Measure the voltage between auto A/C 
control module harness connector terminal 
and chassis ground.

Connector & terminal

(F27) No. 31 (+) — Chassis ground (

−

):

(B282) No. 10 (+) — Chassis ground (

−

):

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

Go to step 3.

3

CHECK POWER SUPPLY FOR PRESSURE 
SWITCH.
1) Turn the ignition switch to OFF.
2) Disconnect the pressure switch harness 
connector.
3) Turn the ignition switch to ON.
4) Measure the voltage between pressure 
switch harness connector terminal and chassis 
ground.

Connector & terminal

(B10) No. 2 (+) — Chassis ground (

−

):

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

Check the harness 
for open or short 
circuit between 
fuse and pressure 
switch.

4

CHECK HARNESS BETWEEN PRESSURE 
SWITCH AND A/C RELAY, AUTO A/C CON-
TROL MODULE.
1) Turn the ignition switch to OFF.
2) Measure the resistance in harness 
between pressure switch connector and A/C 
relay connector.
3) Measure the resistance in harness 
between pressure switch connector and auto 
A/C control module connector.

Connector & terminal

(B10) No. 1 — (F27) No. 31:
(B10) No. 1 — (B282) No. 10:

Is the resistance less than 1 
Ω?

Check the pres-
sure switch. <Ref. 
to AC-41, 
INSPECTION, 
Pressure Switch 
(Triple Pressure 
Switch).>

Repair the har-
ness.

5

CHECK POWER SUPPLY FOR A/C RELAY.
Measure the voltage between A/C relay con-
nector terminal and chassis ground.

Connector & terminal

(F27) No. 28 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 6.

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

6

CHECK A/C RELAY.
Check the A/C relay. <Ref. to AC-40, INSPEC-
TION, Relay and Fuse.>

Is malfunction found in A/C 
relay?

Go to step 7.

Replace the A/C 
relay.

AC(diag)-22

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Diagnostics for A/C System Malfunction

7

CHECK A/C ON SIGNAL.
1) Turn the ignition switch to OFF.
2) Connect the A/C relay and all disconnected 
connectors.
3) Start the engine and turn the A/C switch to 
ON.
4) Turn the temperature control dial at maxi-
mum cool position.
5) Measure the voltage between auto A/C 
control module harness connector terminal 
and chassis ground.

Connector & terminal

(B283) No. 6 (+) — Chassis ground (

−

):

Is the voltage more than 5.5 V? Go to step 9.

Go to step 8.

8

CHECK HARNESS BETWEEN AUTO A/C 
CONTROL MODULE AND ECM.
1) Turn the ignition switch to OFF.
2) Disconnect the harness connector of auto 
A/C control module and ECM.
3) Measure the resistance in harness 
between auto A/C control module connector 
and ECM connector.

Connector & terminal

2.0 L turbo model, 3.0 L model and 2.5 L 
EC, K4, EK model

(B283) No. 6 — (B137) No. 17:

2.0 L non-turbo model and 2.5 L KS, KA 
model

(B283) No. 6 — (B135) No. 20:

Is the resistance less than 1 
Ω?

Replace the auto 
A/C control mod-
ule.

Repair the har-
ness.

9

CHECK MAGNET CLUTCH ON SIGNAL.
1) Stop the engine and turn the A/C switch to 
OFF.
2) Turn the ignition switch to ON.
3) Measure the voltage between ECM con-
nector terminal and chassis ground.

Connector & terminal

2.0 L turbo model, 3.0 L model and 2.5 L 
EC, K4, EK model

(B135) No. 33 (+) — Chassis ground (

−

):

2.0 L non-turbo model and 2.5 L KS, KA 
model

(B135) No. 35 (+) — Chassis ground (

−

):

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

Check the harness 
for open or short 
circuit between A/
C relay and ECM.

10

CHECK MAGNET CLUTCH ON SIGNAL.
1) Start the engine and turn the A/C switch to 
ON.
2) Turn the temperature control dial at maxi-
mum cool position.
3) Measure the voltage between ECM con-
nector terminal and chassis ground.

Connector & terminal

2.0 L turbo model, 3.0 L model and 2.5 L 
EC, K4, EK model

(B135) No. 33 (+) — Chassis ground (

−

):

2.0 L non-turbo model and 2.5 L KS, KA 
model

(B135) No. 35 (+) — Chassis ground (

−

):

Is the voltage 0 V?

Go to step 11.

Replace the ECM.

Step

Check

Yes

No

AC(diag)-23

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Diagnostics for A/C System Malfunction

11

CHECK POWER SUPPLY FOR MAGNET 
CLUTCH.
1) Stop the engine and turn the A/C switch to 
OFF.
2) Disconnect the harness connector of mag-
net clutch.
3) Start the engine and turn the A/C switch to 
ON.
4) Turn the temperature control dial at maxi-
mum cool position.
5) Measure the voltage between magnet 
clutch harness connector terminal and chassis 
ground.

Connector & terminal

(F24) No. 1 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 12.

Check the harness 
for open or short 
circuit between A/
C relay and mag-
net clutch.

12

CHECK HARNESS BETWEEN AUTO A/C 
CONTROL MODULE AND ECM.
1) Stop the engine and turn the A/C switch to 
OFF.
2) Measure the resistance between magnet 
clutch harness connector terminal and chassis 
ground.

Connector & terminal

(F24) No. 2 — Chassis ground:

Is the resistance less than 1 
Ω?

Check the com-
pressor. <Ref. to 
AC-34, INSPEC-
TION, Compres-
sor.>

Repair the har-
ness.

Step

Check

Yes

No

AC(diag)-24

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

Diagnostic Procedure for Actuators

7. Diagnostic Procedure for Actuators

A: INTAKE DOOR ACTUATOR

TROUBLE SYMPTOM:
FRESH/RECIRC mode is not changed.
WIRING DIAGRAM:

AC-01251

B91

MAIN SBF

SBF-6

F/B No.22

7

3

1

B283

B20

B10

B:

B283

B91

B:

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

AUTO A/C

CONTROL MODULE

INTAKE DOOR

ACTUATOR

IGNITION
SWITCH

BATTERY