Subaru Impreza 2004 Service Manual page 22

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
Step
1 CHECK FUSE.
1)Turn the ignition switch to OFF.
2)Remove the No. 2 fuse in main fuse box.
3)Check the condition of fuse.
2 CHECK POWER SUPPLY TO MAGNET
CLUTCH OF A/C COMPRESSOR.
1)Start the engine, and turn A/C switch to ON.
2)Set the temperature control dial to maximum
cold position.
3)Measure the voltage between magnet clutch
connector and chassis ground.
Connector & terminal
(F24) No. 1 (+) — Chassis ground ( − − − − ):
3 CHECK SIGNAL VOLTAGE TO A/C RELAY.
1)Stop the engine, and turn the ignition switch
to ON.
2)Measure the signal voltage between A/C
relay and chassis ground.
Connector & terminal
(F27) No. 12 (+) — Chassis ground ( − − − − ):
4 CHECK A/C RELAY.
1)Remove the A/C relay in main fuse box.
2)Check the A/C relay. <Ref. to AC-37,
INSPECTION, Relay and Fuse.>
5 CHECK OPERATION OF MAIN FAN MOTOR.
1)Start the engine.
2)Turn the A/C switch to ON.
3)Check the operation of main fan motor.
6 CHECK POWER SUPPLY TO MAIN FAN MO-
TOR.
CAUTION:
Be careful not to overheat the engine during
repair.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from main fan
motor.
3)Start the engine, and warm it up until engine
coolant temperature increases over 95°C
(203°F).
4)Stop the engine and turn ignition switch to
ON.
5)Measure the voltage between main fan
motor connector and chassis ground.
Connector & terminal
DOHC Turbo model:
(F17) No. 1, 2 (+) — Chassis ground ( − − − − ):
Non-turbo model:
(F17) No. 2 (+) — Chassis ground ( − − − − ):
7 CHECK GROUND CIRCUIT OF MAIN FAN
MOTOR.
1)Turn the ignition switch to OFF.
2)Measure the resistance between main fan
motor connector and chassis ground.
Connector & terminal
DOHC Turbo model:
(F17) No. 3, 4 — Chassis ground:
SOHC model:
(F17) No. 1 — Chassis ground:
Diagnostics for A/C System Malfunction
Is the fuse blown-out?
Is the voltage more than 10 V? Go to step 3.
Is the voltage more than 10 V? Go to step 4.
Is the operation of the relay
OK?
Does the radiator main fan
operate?
Is the voltage more than 10 V? Go to step 7.
Is the resistance less than 1
Ω?
AC(diag)-20
Check
Replace the fuse.
Go to step 5.
Go to step 10.
Go to step 8.
Yes No
Go to step 2.
Repair the open
circuit in harness
for power supply
line of the A/C
compressor.
Repair the open
circuit in harness
for A/C relay signal
circuit.
Replace the A/C
relay.
Go to step 6.
Repair the open
circuit in harness
for power supply
circuit.
Repair the open
circuit in harness
between main fan
motor connector
and chassis
ground.