Subaru Impreza 2004 Service Manual page 32

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
Step
1 CHECK AMBIENT SENSOR.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from ambient sen-
sor.
3)Measure the resistance between connector
terminals of ambient sensor.
Terminals
No. 1 — No. 2:
2 CHECK INPUT SIGNALS FOR AMBIENT
SENSOR.
1)Turn the ignition ON.
2)Measure the voltage between (F78) connec-
tor terminals.
Connector & terminal
LHD model:
(F78) No. 1 (+) — No. 2 ( − − − − ):
RHD model:
(F78) No. 2 (+) — No. 1 ( − − − − ):
3 CHECK OUTPUT SIGNALS FROM A/C CON-
TROL MODULE.
1)Turn the ignition switch to OFF.
2)Pull out the A/C control unit.
3)Disconnect the connector from ambient sen-
sor.
4)Turn the ignition switch to ON.
5)Measure the voltage between connector ter-
minals of A/C control module.
Connector & terminal
(B283) No. 9 (+) — No. 17 ( − − − − ):
4 CHECK HARNESS CONNECTOR BETWEEN
A/C CONTROL MODULE AND AMBIENT
SENSOR.
1)Turn the ignition switch to OFF.
2)Disconnect the connectors from A/C control
module.
3)Measure the resistance of harness between
A/C control module and ambient sensor.
Connector & terminal
LHD model:
(F78) No. 1 — (B283) No. 9:
RHD model:
(F78) No. 2 — (B283) No. 9:
5 CHECK HARNESS CONNECTOR BETWEEN
A/C CONTROL MODULE AND AMBIENT
SENSOR.
Measure the resistance of harness between A/
C control module and ambient sensor.
Connector & terminal
LHD model:
(F78) No. 2 — (B283) No. 17:
RHD model:
(F78) No. 1 — (B283) No. 17:
6 CHECK POOR CONTACT.
Check poor contact in A/C control module con-
nector.
Diagnostic Procedure for Sensors
Is the resistance approx. 2.2
kΩ at 25°C (77°F)?
Is the voltage approx. 5 V?
Is the voltage approx. 5 V?
Is the resistance less than 1
Ω?
Is the resistance less than 1
Ω?
Is there poor contact in con-
nector?
AC(diag)-30
Check
Go to step 2.
Go to step 6.
Go to step 4.
Go to step 5.
Go to step 6.
Repair the con-
nector.
Yes No
Replace the ambi-
ent sensor.
Go to step 3.
Go to step 6.
Repair the open
circuit in harness
between A/C con-
trol module and
ambient sensor.
Repair the open
circuit in harness
between A/C con-
trol module and
ambient sensor.
Replace the A/C
control module.