Subaru Legacy IV (2008 year). Manual - part 987

AC-51

General Diagnostic Table

HVAC SYSTEM (HEATER, VENTILATOR AND A/C)

30.General Diagnostic Table

A: INSPECTION

Symptoms

Repair order

Blower motor

Does not operate.

Fuse

Blower motor relay

Blower motor

Blower motor resistor (Manual A/C)

Blower switch

Wiring harness

Strange noise

Blower motor

Compressor

Does not operate.

Refrigerant

Fuses

Air conditioning relay

Magnet clutch

Compressor

Pressure switch

A/C switch

Blower switch

Wiring harness

Strange noise

V-belt

Magnet clutch

Compressor

Belt tension adjuster

Cold air not emitted.

Refrigerant

V-belt

Magnet clutch

Compressor

Pressure switch

Aspirator hose (Auto A/C)

Blower fan relay

Blower motor

A/C switch

Blower switch

Control module

Expansion valve

Evaporator

Air mix actuator (Auto A/C)

Temperature control cable (Manual A/C)

Wiring harness

Heater duct

Heater vent duct

Warm air not emitted.

Engine coolant

Aspirator hose (Auto A/C)

Air mix actuator (Auto A/C)

Temperature control cable (Manual A/C)

Blower switch

Heater core

AC-52

General Diagnostic Table

HVAC SYSTEM (HEATER, VENTILATOR AND A/C)

Temperature of air from vents does not change.

Engine coolant

Air mix actuator (Auto A/C)

Temperature control cable (Manual A/C)

Temperature control switch (Auto A/C)

Wiring harness (Auto A/C)

Unable to switch blow vents.

Mode actuator (Auto A/C)

Mode switch cable (Manual A/C)

Mode switch (Auto A/C)

Wiring harness (Auto A/C)

Unable to switch suction vents.

FRESH/RECIRC switch (Auto A/C)

FRESH/RECIRC actuator (Auto A/C)

Wiring harness (Auto A/C)

Symptoms

Repair order

AC(diag)-2

Basic Diagnostic Procedure

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

1. Basic Diagnostic Procedure

A: PROCEDURE

Step

Check

Yes

No

1

START INSPECTIONS.
1) Perform the pre-inspection. <Ref. to 
AC(diag)-3, INSPECTION, General Descrip-
tion.>
2) Perform the self-diagnosis. <Ref. to 
AC(diag)-9, OPERATION, Diagnostic Chart for 
Self-Diagnosis.>

Does the self-diagnosis oper-
ate?

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

IDENTIFY MALFUNCTION PART.
Identify the malfunction part with self-diagnosis.

Can the malfunction part be 
confirmed?

Repair the mal-
functioning part in 
accordance with 
each diagnostic 
chart.

Go to step 3.

3

CHECK COMPARTMENT TEMPERATURE.
1) Turn on the A/C switch.
2) Turn the temperature control dial at maxi-
mum cool position.
3) Check the compartment temperature 
change.

Does the compartment temper-
ature change?

Go to step 4.

<Ref. to AC(diag)-
18, COMPART-
MENT TEMPERA-
TURE DOES NOT 
CHANGE, OR A/C 
SYSTEM DOES 
NOT RESPOND 
PROMPTLY, Diag-
nostics for A/C 
System Malfunc-
tion.>

4

CHECK A/C SYSTEM RESPONSE.
Change the temperature setting, and check the 
response of A/C system.

Does the A/C system respond 
quickly?

A/C system is nor-
mal.

<Ref. to AC(diag)-
18, COMPART-
MENT TEMPERA-
TURE DOES NOT 
CHANGE, OR A/C 
SYSTEM DOES 
NOT RESPOND 
PROMPTLY, Diag-
nostics for A/C 
System Malfunc-
tion.>

AC(diag)-3

General Description

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

2. General Description

A: CAUTION

1) Never connect the battery in reverse polarity.
Doing so may immediately damage the auto A/C
control module.
2) Do not disconnect the battery terminals while the
engine is running. A large counter electromotive
force will be generated in the generator, and this
voltage may damage electronic parts such as auto
A/C control module etc.
3) Before disconnecting the connectors of sensors
and the auto A/C control module, be sure to turn off
the ignition switch. Auto A/C control module may be
damaged.
4) Every A/C-related part is a precision part. Do not
drop them.
5) Airbag system wiring harness is routed near the
A/C control panel and junction box.

CAUTION:
• Do not use electrical test equipment on wir-
ing harness and connector circuits of the air-
bag system.
• Be careful not to damage the airbag system
wiring harness when servicing the A/C control
panel and junction box.

B: INSPECTION

Before performing the diagnosis, check the follow-
ing items which may cause problems in the A/C
system.

1. BATTERY

1) Measure the battery voltage and specific gravity
of electrolyte.

Standard voltage: 12 V

Specific gravity: 1.260 or more
2) Check the condition of the fuses for A/C system
power supply and other fuses.
3) Check the condition of harness and harness
connector connections.

2. ASPIRATOR HOSE

1) Turn the ignition switch to ON, and press the A/
C switch.
2) Turn the temperature control dial to maximum
hot position.
3) Turn the air flow control dial to “DEF” position.
4) Turn the fan speed control dial to “MAX” posi-
tion.
5) Put a strip of paper close to the front side of in-
vehicle sensor suction port (A) located in the driv-
er’s side console side panel, and check that air is
being sucked into the port by seeing the paper
moving towards the port.

NOTE:
Be careful not to let the paper get sucked into the
port.

6) If the paper does not move at all, remove the
driver’s side console side panel <Ref. to EI-55, RE-
MOVAL, Center Console.> and check for improper
connection of the aspirator hose, in-vehicle sensor
and heater unit, and repair them if necessary.

3. A/C LINE

Check the connection for A/C line (A) and lower
side high-pressure pipe.

4. CONTROL LINKAGE

1) Check the state of mode door linkage.
2) Check the state of air mix door linkage.
3) Check the state of FRESH/RECIRC door link-
age.

AC-01188

(A)

(A)

AC-00895