Trying to Regain HVAC Function After 12V Terminal Reverse

Discussion in 'Gen 3 Prius Technical Discussion' started by wilt0048, Sep 17, 2025 at 3:14 PM.

  1. wilt0048

    wilt0048 New Member

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    As the title says, I carelessly crossed 12v battery terminals during replacement. I've replaced half a dozen fuses, the big 125DC/DC under the front panel. None of the A/C related/labeled fuses were blown in the engine panel or in the cabin panel, yet I've got nothing at the A/C instrument panel (plasmacluster). No lights, no signs of life, which leads me to believe it's not getting power, just not sure what circuit that would be. I've seen mention on a big HVAC fuse in the inverter, but would 12v power interact with that? ECU damage? The only other weird thing going on is there's a cooling fan that now comes on when the car turns on and stays running continuously. Thanks to everyone that contributes to this forum, searching through the mass of knowledge has got me this far, but I'm at a dead end now.
     
    #1 wilt0048, Sep 17, 2025 at 3:14 PM
  2. Tombukt2

    Tombukt2 Senior Member

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    The fan that is continuously running is in the back of the car right next to your hybrid battery I'm going to guess if not figured out need go back and listen . If so you a hybrid electric issue . And the computers put the fan on thinking the battery is under massive stress or something similar why that is . We need find out.
     
    #2 Tombukt2, Sep 18, 2025 at 9:11 AM
  3. ChapmanF

    ChapmanF Senior Member

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    #3 ChapmanF, Sep 18, 2025 at 7:13 PM
  4. rjparker

    rjparker Tu Humilde Sirviente

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    I would check power feeding that panel, not just if the 10amp AC fuse is good. Use a meter on that fuse.
    IMG_9892.jpeg

    If power is not there use a meter to find the problem which is either the 125a fuse, connectors not made well after changing the 125a, the IG1 No 1 Relay or its coil control.
    Image.jpeg
    I would also check these AC Amplifier Fuses IMG_9889.jpeg

    There are other modules involved but this gets you some direction.
     
    #4 rjparker, Sep 18, 2025 at 10:44 PM
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