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Old 10-13-2014, 04:14 PM   #1
snkfischer
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Default 2008 Impreza A/C IG fuse keeps blowing

If someone has posted something like this before, apologies. I couldn't find anything specific to my issue in the forums.

I have a 2008 Subaru 2.5i sedan. Recently, the interior fans would not run when I went to turn them on (manual A/C). When I went to look at the fuses, the A/C IG fuse (fuse 20 on the wiring diagram) was blown. Also, I noticed that the cigarette lighter fuse was blown, but I never used it (used the accessory one for charging phones, etc). I put another fuse in, started the car, turned the fan on and *click* - IMMEDIATELY blew the fuse. Now I can't run the heater, and we're heading into the season where I'll need to defrost the windows.

No other fuses are blown, including the blower motor fan fuses.

Here's the strange thing - when the car is not started, but with the key running the accessories, the fans will work fine with a new fuse in the A/C IG slot. As soon as the car is started and idling, when you turn on the fans, the fuse immediately blows. It doesn't even attempt to run the fans.

I'm a little at a loss as to how to troubleshoot this. Would it be a bad fan switch, or something else? I don't understand why it would work when the car is "off", but then short out when the car is on and idling. Also - the other fuses are fine, including the cigarette lighter fuse. That must have been a coincidence.

Any help thinking through what's going on is appreciated. Thanks!
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Old 10-13-2014, 08:44 PM   #2
snkfischer
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So more troubleshooting and several blown fuses later...

With a new fuse in and running the blower, it will work on all settings, except when I turn the left dial (which directs the air flow from feet, to chest, both, or front defogger, etc.) EXCEPT for the two most clockwise positions which engage the defogger (front windshield vents). When that setting is switched to, the fuse immediately blows.

What confuses me is that left switch has no electrical connections at all - just a cable (like a bicycle brake) that must be opening and closing vents/air paths. Is something being engaged electrically as well when the defogger / windshield setting is engaged?
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Old 10-14-2014, 01:01 AM   #3
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My thought is that the cable mechanism is contacting the power wires to the blower when you move it. Check out the cable mechanism and see if there are some wires getting interfered with.
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Old 10-15-2014, 01:33 PM   #4
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Thanks for the advice.

After spending a long night teaching myself electrical theory and how to read wiring diagrams, I'm thinking that the issue might be a potential short in the intake door actuator. I'm going to be taking the dash complete off tomorrow and take a look. Or, you could be complete correct and the wires might be shorting against the cable when it's moved.
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Old 10-15-2014, 05:59 PM   #5
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If there is a switch being activated by the cable mechanism I could see what you say being a possibility. The switch could be turning power on to an area that has a short issue. If there is no switch involved then I could see the wiring is getting shorted by mechanism itself. Try disconnecting connectors you can get access at to see if the short goes away and help lead you to the trouble. You could use a brake light bulb in place of the fuse to limit the current to a safe level by soldering some wires to the bulb and a bad fuse. If the light gets real bright during the testing then the short is most likely still there.

Last edited by Cougar4; 10-16-2014 at 11:38 AM.
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Old 10-21-2014, 09:06 AM   #6
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Found the issue. The A/C compressor bearings were shot (even when the magnetic clutch was disengaged. This caused the unit to get so hot that it fused the wire to the housing, causing a short. It also tore off the A/C compressor belt.

I discovered that when the defogger is engaged, it activates the A/C relay. When this happened, the fuse snapped due to the short on the compressor.
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Old 10-21-2014, 12:02 PM   #7
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Glad you found the problem. Thanks for the update.
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Old 11-30-2014, 02:57 AM   #8
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this might be the exact same problem i am trying to figure out, i will go check my sti right now. cougar4 has been awesome via pm in trying to figure this out with me
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Old 11-30-2014, 12:01 PM   #9
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Quote:
Originally Posted by XgT View Post
this might be the exact same problem i am trying to figure out, i will go check my sti right now. cougar4 has been awesome via pm in trying to figure this out with me
It very well could be the same issue causing your problem but even if isn't we'll find the little trouble maker.
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Old 11-30-2014, 05:54 PM   #10
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so my problem with blowing the ac/ig fuse when ignition is on is still there, if anyone has any suggestions as what could be causing it please chime in, it would be greatly appreciated.
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Old 11-30-2014, 10:03 PM   #11
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It may help if you could post a picture of the fuse panel and point out which fuse position has the trouble on it. We seem seem to be looking in the wrong areas for the trouble.
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Old 03-02-2015, 09:06 PM   #12
Hando567
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Duplicate reply deleted.

Last edited by Hando567; 03-02-2015 at 09:16 PM. Reason: delete duplicate reply.
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Old 03-02-2015, 09:08 PM   #13
Hando567
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This thread was extremely helpful for my 2008 Imprezza 2.5i. The A/C compressor started making a rattling noise yesterday, and then today when I turned the fan select to the front defroster the a/c IG fuse blew. I did not connect the problems until I read this thread. The fan works fine on all settings except defrost. Thank you all for sharing and saving me many hours of troubleshooting!
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