Subaru Legacy (2005 year). Service manual — part 871
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
AC(diag)
Page
Basic Diagnostic Procedure . . . . . . . . . . . . . . . . . . 2
General Description . . . . . . . . . . . . . . . . . . . . . 3
Electrical Component Location . . . . . . . . . . . . . . . . ...5
Auto A/C Control Module I/O Signal. . . . . . . . . . . . . . . 8
Diagnostic Chart for Self-Diagnosis . . . . . . . . . . . . . . ..10
Diagnostics for A/C System Malfunction . . . . . . . . . . . . ...15
Diagnostic Procedure for Actuators . . . . . . . . . . . . . . ..24
Diagnostic Procedure for Sensors . . . . . . . . . . . . . . . 30
Diagnostics with Phenomenon. . . . . . . . . . . . . . . . ..41
AC(diag)-2
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
Basic Diagnostic Procedure
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)-10, OPERATION, Diagnostic Chart
for Self-Diagnosis.>
Does the self-diagnosis oper-
ate?
2
IDENTIFY MALFUNCTION PART.
Identify the malfunction part with self-diagno-
sis.
Can the malfunction part be
identified?
Repair the mal-
function part in
accordance with
each diagnostic
chart.
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 tem-
perature change?
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.
AC(diag)-3
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
General Description
2. General Description
A: CAUTION
1) Never connect the battery in reverse polarity.
• Auto A/C control module may be destroyed in-
stantly.
2) Do not disconnect the battery terminals while the
engine is running.
• A large counter electromotive force will be gener-
ated in the generator, and this voltage may damage
electronic parts such as auto A/C control module,
etc.
3) Before disconnecting the connectors of each
sensor 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:
• For airbag system, yellow-colored wiring har-
ness and connectors are used. Do not use the
electrical test equipment on these circuits.
• 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 might affect A/C system problems.
1. BATTERY
1) Measure the battery voltage and specific gravity
of electrolyte.
Standard voltage: 12 V
Specific gravity: More than 1.260
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 at maximum
hot position.
3) Turn the air flow control dial to “DEF” position.
4) Turn the fan speed control dial to 4th position.
5) Approach a strip of paper in front of the in-vehi-
cle sensor suction port (A) located in the instrument
lower cover, 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 in-
strument panel lower cover <Ref. to EI-50, RE-
MOVAL, Instrument Panel Lower Cover.> and
check for improper connection of the aspirator hose
(A), 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 intake door linkage.
(A)
AC-00894
AC-00810
(A)
(A)
AC-00895
AC(diag)-4
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
General Description
5. CONTROL SWITCHES
Start and warm-up the engine completely.
1) Inspection using switches
2) Compressor operation inspection
3) Inspection of illumination control
No.
Point to check
Switch operation
Judgment standard
1
OFF switch
Press the OFF switch.
Setting temperature display goes out.
• Blower fan: OFF
• Inlet opening: FRESH
• Compressor: OFF
2
AUTO switch
1) Press the AUTO switch.
2) Turn the temperature control dial to the left
fully, and set to 18
°C (maximum cool position).
AUTO display illuminates.
• Outlet air temperature: COOL
• Blower fan: HI (AUTO)
• Outlet opening: FACE
• Inlet opening: AUTO
• Compressor: AUTO
3) Turn the temperature control dial to the right
slowly, and change the setting from 18
°C (maxi-
mum cool position) to 32
°C.
• Outlet air temperature: COOL
→ HOT
• Blower fan: AUTO
• Outlet opening: FACE
→ B/L → FOOT
• Inlet opening: AUTO
• Compressor: AUTO
4) Turn the temperature control dial to the right
fully, and set to 32
°C (maximum hot position).
• Outlet air temperature: HOT
• Blower fan: HI (AUTO)
• Outlet opening: FOOT
• Inlet opening: FRESH (AUTO)
• Compressor: AUTO
3
Defroster switch
Press the defroster switch.
Defroster switch indicator illuminates.
• Outlet air temperature: AUTO
• Blower fan: AUTO
• Outlet opening: DEF
• Inlet opening: FRESH
• Compressor: ON
4
FRESH/RECIRC
switch
Press the FRESH/RECIRC switch.
Inlet opening switches RECIRC
→ FRESH or
FRESH
→ RECIRC each time pressing the
switch.
5
MODE switch
Press the MODE switch.
Outlet opening switches FACE
→ B/L →
FOOT
→ F/D each time pressing the switch
6
FAN switch
Press the FAN (+) switch.
Inlet opening switches LO
→ M1 → M2 → M3
→ M4 → HI each time pressing the switch
No.
Point to check
Switch operation
Judgment standard
1
Compressor
1) Turn the A/C switch to ON.
2) Set the FAN switch between LO and HI.
Compressor: ON
No.
Point to check
Switch operation
Judgment standard
1
Illumination
Turn the lighting switch to ON.
Illumination comes on.
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