Subaru 2009 IMPREZA Service Manual page 2749

HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
Step
1 CHECK FUSE.
1) Turn the ignition switch to OFF.
2) Remove the fuse No. 22 from fuse & relay
box.
3) Check the condition of fuse.
2 CHECK SIGNAL TO A/C RELAY AND AUTO
A/C CONTROL MODULE.
1) Disconnect the A/C relay and auto A/C con-
trol module harness connector.
2) Turn the ignition switch to ON.
3) Measure the voltage between A/C relay
connector terminal and chassis ground.
4) Measure the voltage between auto A/C con-
trol module harness connector terminal and
chassis ground.
Connector & terminal
(F27) No. 17 (+) — Chassis ground (–):
(i88) No. 11 (+) — Chassis ground (–):
3 CHECK POWER SUPPLY FOR PRESSURE
SWITCH.
1) Turn the ignition switch to OFF.
2) Disconnect the pressure switch harness
connector.
3) Turn the ignition switch to ON.
4) Measure the voltage between pressure
switch harness connector terminal and chassis
ground.
Connector & terminal
(B10) No. 2 (+) — Chassis ground (–):
4 CHECK HARNESS BETWEEN PRESSURE
SWITCH AND A/C RELAY, AUTO A/C CON-
TROL MODULE.
1) Turn the ignition switch to OFF.
2) Measure the resistance of harness between
pressure switch connector and A/C relay con-
nector.
3) Measure the resistance of harness between
pressure switch connector and auto A/C control
module connector.
Connector & terminal
(B10) No. 2 — (F27) No. 17:
(B10) No. 2 — (i88) No. 11:
5 CHECK POWER SUPPLY FOR A/C RELAY.
Measure the voltage between A/C relay con-
nector terminal and chassis ground.
Connector & terminal
(F27) No. 14 (+) — Chassis ground (–):
6 CHECK A/C RELAY.
Check the A/C relay. <Ref. to AC-39, INSPEC-
TION, Relay and Fuse.>
Diagnostics for A/C System Malfunction
Is the fuse blown out?
Is the voltage 10 V or more?
Is the voltage 10 V or more?
Is the resistance less than 1 ? Check the pres-
Is the voltage 10 V or more?
Is the A/C relay OK?
AC(diag)-20
Check Yes
Replace the fuse.
Go to step 5.
Go to step 4.
sure switch. <Ref.
to AC-40, INSPEC-
TION, Pressure
Switch (Triple
Pressure Switch).>
Go to step 6.
Go to step 7.
No
Go to step 2.
Go to step 3.
Check for open or
short circuit in the
harness between
fuse and pressure
switch.
Repair the har-
ness.
Check open or
short circuit of har-
ness between fuse
and A/C relay.
Replace the A/C
relay.