2003 WRX - Lights Dimming When AC/Defog Compressor Engages
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This is a discussion on 2003 WRX - Lights Dimming When AC/Defog Compressor Engages within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hi guys, I'm having an issue with my interior/exterior lights dimming whenever my 2003 WRX engages the AC/defog compressor. The ...

  1. #1
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    2003 WRX - Lights Dimming When AC/Defog Compressor Engages

    Hi guys,

    I'm having an issue with my interior/exterior lights dimming whenever my 2003 WRX engages the AC/defog compressor. The lights will typically dim for 2-3 seconds every time the compressor is engaged. Engine noise also appears to be dampened during the dimming but RPM is NOT affected. The car has shut off once during heavy traffic but quickly restarted.

    The facts:

    - 2003 WRX 100% Stock with the exception of a combo sub/amp I have installed under the seat in place of the stock sub.
    - 86K Miles
    - Voltage tested with a multimeter...100% normal readings even when lights dim

    What I've tried:

    - Cleaning battery/tightening terminal connections/removing corrosion: No effect
    - Checking/cleaning grounds on both fenders: No effect
    - Replaced battery: No effect
    - Replaced Alternator: No effect
    - Disconnecting sub/amp lead from battery: No effect

    Any help is GREATLY appreciated!

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  3. #2
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    Hello again fellow WRX owners,

    Again, any help is appreciated...almost at 200 thread views here.

  4. #3
    \_(ツ)_/ Rambo's Avatar
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    It certainly sounds like you've done due diligence in your troubleshooting, so I don't have much to add, unfortunately. The alternator would be my first suspect, but you've eliminated that. I'd also be suspect of the AC compressor clutch, but if you insist there's no RPM drop, perhaps not. Pulling an ECU log with a tool like a Tactrix cable would give you higher resolution to the voltage and RPM impact when driving than looking at the gauge cluster.

    How much are the lights dimming? I notice my lights dim slightly when the AC kicks on on my 2003. I can clearly feel the compressor clutch engage and the engine lug down (just a bit), and that's with Stage II power modfications, so it is a significant parasitic loss on the drivetrain. If it's a slight dimming, I wouldn't be concerned, but if it's enough to inhibit night vision, I'd continue on your troubleshooting path investigating all electrical circuits involved.

    Sorry I can't give you more, man. You're doing the right things, though.
    Isaac -- 2003 WRX sedan Stg II - Gave its life for mine 6/2013.
    2007 Outback 3.0R wagon
    Proud owner of a N.E.R.D, Member 1.3810-23

    The pursuit of knowledge is hopeless and eternal... Hooray!!! - Professor Farnsworth

  5. #4
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    Hi Rambo,

    Thanks for the support and insight! The dimming is noticeable but not drastic (I know this is kind of subjective). It really came to my attention when I was stuck in traffic and my WRX appeared to shut down after light dimming. It is reassuring to hear that I'm not the only owner with dimming headlights and I suppose it's not as big a deal as I'm making it out to be.

  6. #5
    \_(ツ)_/ Rambo's Avatar
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    Keep in mind it's only a slight dim for me, and only noticeable when my lights are glaring against the back of another car (such as at a stoplight). In this situtation, the car is also idling, so the RPM impact during the compressor cycling is more noticeable compared to cruising at 2-3k RPM.
    Isaac -- 2003 WRX sedan Stg II - Gave its life for mine 6/2013.
    2007 Outback 3.0R wagon
    Proud owner of a N.E.R.D, Member 1.3810-23

    The pursuit of knowledge is hopeless and eternal... Hooray!!! - Professor Farnsworth

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