Subaru Legacy III (2000-2003 year). Manual - part 867

AC-4

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

BASIC DIAGNOSTIC PROCEDURE

6

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

A/C system responds quickly.

A/C system is OK. LHD: <Ref. to AC-

24, COMPART-
MENT TEMPERA-
TURE DOES NOT 
CHANGE FROM 
“SET” TEMPERA-
TURE OR AIR 
CONDITIONING 
SYSTEM DOES 
NOT RESPOND 
QUICKLY, Diag-
nostics for A/C 
System Failure 
(LHD Model).>  
RHD: <Ref. to AC-
44, COMPART-
MENT TEMPERA-
TURE DOES NOT 
CHANGE FROM 
“SET” TEMPERA-
TURE OR AIR 
CONDITIONING 
SYSTEM DOES 
NOT RESPOND 
QUICKLY, Diag-
nostics for A/C 
System Failure 
(RHD Model).>  

Step

Value

Yes

No

AC-5

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

GENERAL DESCRIPTION

2. General Description

A: CAUTION

1) Never connect the battery in reverse polarity.
• The auto A/C control module may be destroyed
instantly.
2) Do not disconnect the battery terminals while the
engine is running.
• A large counter electromotive force will be gener-
ated in the alternator, and this voltage may damage
electronic parts such as A/C control module.
3) Before disconnecting the connectors of each
sensor and the A/C control module, be sure to turn
off the ignition switch.
• Otherwise, the Auto A/C control module may be
damaged.
4) Every auto 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 (A/C control module) and junction
box.

CAUTION:
• All airbag system wiring harness and con-
nectors are colored yellow. Do not use electri-
cal test equipment on these circuits.
• Be careful not to damage Airbag system wir-
ing harness when servicing the A/C control
panel (A/C control module) and junction box.

B: INSPECTION

Before performing diagnosis, check the following
items which might affect engine problems.

1. BATTERY

1) Measure battery voltage and specific gravity of
electrolyte.

Standard voltage: 12 V

Specific gravity: Above 1.260
2) Check the condition of the fuses for A/C, heater
and other fuses.

3) Check the condition of the harnesses and har-
ness connectors connection.

2. ASPIRATOR HOSE

1) Turn ignition switch to ON.
2) Push “DEF” switch and then blower fan switch to
turn the blower fan to maximum speed.

3) Firmly hold a thin thread (b) in front of the in-ve-
hicle sensor suction port (a) for the auto A/C control
unit and check that the thread moves towards the
port indicating that air is being sucked into the port.

NOTE:
• Ensure the thread does not get sucked into the
port.

4) If the thread does not move at all, remove the
auto A/C control unit  <Ref. to AC-34, REMOVAL,
Control Unit.> and check for improper connection
of the aspirator hose (a) and auto A/C control unit
and secure as necessary.

(a) Main fuse box

( a )

AC-00309

AC-00310

AUTO

OFF

A/C

OUT.TEMP

AC-00311

( a )

( b )

AC-00312

( a )

AC-6

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

GENERAL DESCRIPTION

3. REFRIGERANT LINE

Check contact for refrigerant line (A).

4. CONTROL LINKAGE

1) Check state of mode door control rod and link-
age.
2) Check state of air mix door control rod and link-
age.
3) Check state of intake door control rod and link-
age.

(a) Control rod

( A )

AC-00313

AC-00314

( a )

AC-7

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)

GENERAL DESCRIPTION

5. CONTROL SWITCHES

Start and warm up engine completely.
1) Inspection using switches.

2) Compressor operation inspection

3) Illumination control inspection

No.

Point to check

Switch operation

Judgement standard

1

OFF switch

OFF switch “ON”

“SET” temperature display go out.
• Air flow 

→

 OFF

• Outlet 

→

 HEAT

• Inlet 

→

 FRESH

• Compressor 

→

 OFF

2

AUTO switch

A. AUTO switch “ON”
B. Temp. control dial 18

°

C (65

°

F) (Max. 

Cold)

a. AUTO switch display illuminates.
b.
• Outlet air 

→

 Cool

• Air flow 

→

 HI (AUTO)

• Outlet 

→

 VENT

• Inlet 

→

 AUTO

• Compressor 

→

 AUTO

C. TEMP control dial is gradually set from 
18

°

C (65

°

F) to 32

°

C (85

°

F).

c. Air and air outlet mode change as follows:
• Outlet air: cool 

→

 hot

• Air flow: AUTO
• Outlet: VENT 

→

 BI-LEVEL 

→

 HEAT

• Inlet: AUTO

D. Temp. control dial 32

°

C (85

°

F) (Max. Hot)

d. Outlet air 

→

 Hot

• Air flow 

→

 HI (AUTO)

• Outlet 

→

 HEAT

• Inlet 

→

 FRESH (AUTO)

• Compressor 

→

 AUTO

3

DEF switch

A. DEF switch “ON”
B. Temp. control dial 18 — 32

°

C (65 — 85

°

F)

a. DEF switch display illuminates.
b.
• Outlet air temperature (AUTO control)
• Air flow (AUTO control)
• Outlet 

→

 DEF

• Inlet 

→

 FRESH

• Compressor 

→

 ON

4

FRESH/RECIRC 
switch

FRESH/RECIRC switch “ON”

Changes from RECIRC 

→

 FRESH, or FRESH 

→

 

RECIRC.

5

MODE switch

MODE switch “ON”

Outlet changes from VENT 

→

 BI-LEVEL 

→

 HEAT 

→

 

DEF/HEAT each time MODE switch is pushed.

6

FAN switch

FAN switch “ON”

Fan speed changes from LO 

→

 M1 

→

 M2 

→

 HI each 

time FAN switch is pushed.

7

OUT-TEMP 
switch

OUT-TEMP switch “ON”

Ambient temperature flashes on “set” temperature dis-
play, and “set” temperature appears.

No.

Point to check

Switch operation

Judgement standard

Remarks

1

Compressor

A. AUTO switch “ON”
B. A/C switch “ON”
C. DEF switch “ON”

a. Compressor ON
b. Compressor ON
c. Compressor ON

Compressor turns OFF several 
seconds after AUTO switch is 
turned ON.

No.

Point to check

Switch operation

Judgement standard

Remarks

1

Illumination

Lighting switch “ON”

Illumination light illuminates and both switch 
light and “set” temperature display dim.

Green lights remain on although 
OFF and OUT-TEMP switches 
remain ON.

Press OFF switch 
longer than 1 second.

Dimming of illumination is canceled.