Subaru Impreza 2004 Service Manual page 28

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
Step
1 CHECK POWER SUPPLY FOR AUTO A/C
CONTROL MODULE SIDE.
1)Turn the ignition switch to ON.
2)Turn the A/C switch to ON.
3)Measure the voltage between auto A/C con-
trol module harness connector terminal and
chassis ground.
Connector & terminal
(B283) No. 6 (+) — Chassis ground ( − − − − ):
2 CHECK POWER SUPPLY FOR ACTUATOR
SIDE.
Measure the voltage between mode door actu-
ator harness connector terminal and chassis
ground.
Connector & terminal
(B77) No. 1 (+) — Chassis ground ( − − − − ):
3 CHECK SIGNAL FOR AUTO A/C CONTROL
MODULE SIDE.
Measure the voltage between auto A/C control
module harness connector terminal and chas-
sis ground with oscilloscope.
Connector & terminal
(B282) No. 12 (+) — Chassis ground ( − − − − ):
4 CHECK SIGNAL FOR ACTUATOR SIDE.
Measure the voltage between mode door actu-
ator harness connector terminal and chassis
ground.
Connector & terminal
(B77) No. 3 (+) — Chassis ground ( − − − − ):
5 CHECK GROUND CIRCUIT OF ACTUATOR.
1)Turn the ignition switch and A/C switch to
OFF.
2)Measure the resistance between mode door
actuator harness connector terminal and chas-
sis ground.
Connector & terminal
(B77) No. 2 — Chassis ground:
6 CHECK POOR CONTACT.
Check poor contact in auto A/C control module
connector.
Diagnostic Procedure for Actuators
Is the voltage more than 10 V? Go to step 2.
Is the voltage more than 10 V? Go to step 3.
Is the voltage approx. 5.5 V?
Is the voltage approx. 5.5 V?
Is the resistance less than 1
Ω?
Is there poor contact in con-
nector?
AC(diag)-26
Check
Go to step 4.
Go to step 5.
Go to step 6.
Repair the con-
nector.
Yes No
Replace the auto
A/C control mod-
ule.
Repair the open
circuit in harness
between auto A/C
control module
and mode door
actuator.
Replace the auto
A/C control mod-
ule.
Repair the open
circuit in harness
between auto A/C
control module
and mode door
actuator.
Repair the open
circuit in harness
between mode
door actuator and
chassis ground.
Replace the A/C
control module.