1. Attachments are working again! Check out this thread for more details and to report any other bugs.

A/C blower motor stays on, even when car is off

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by BigFatGuy, Mar 15, 2021.

  1. BigFatGuy

    BigFatGuy Member

    Joined:
    Mar 11, 2011
    50
    42
    0
    Location:
    Oklahoma City
    Vehicle:
    2007 Prius
    Model:
    N/A
    Weird one here.
    2013 Prius base, ~140,000 miles, the blower motor went out summer 2020. I replaced it with a new unit, super easy job and it's worked great ever since.
    Four days ago, wife came home in it, parked in the garage and thought she heard it making noise, but thought it was an engine cooling fan that would shut off soon. 24 hours later, I go out to the garage and notice a low fan noise from her car. Getting in, the blower motor is blowing ambient temp air through the a/c vents, and it's been doing it for a full day, with the car off and the key ~100ft away. -_-
    We pulled the power connector from the blower to get it to stop, but that's a temp fix. I thought it might be the blower motor resistor, but this car doesn't seem to have one. Any ideas?
     
  2. tankyuong

    tankyuong Senior Member

    Joined:
    Nov 9, 2012
    1,555
    659
    0
    Location:
    Central MO
    Vehicle:
    2012 Prius c
    Model:
    II
    Check the 12v battery
     
    BigFatGuy likes this.
  3. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Well, that's sort of entertaining.

    At first I would have bet that the power supply to the blower was switched with the ignition and so that Couldn't Happen.

    But according to the diagram, the power coming in on the black wire (position 3) comes from a fuse that has power always.

    L33.png

    The blue wire, position 2, carries a variable pulse train that is sent by the A/C amplifier, telling the blower how fast to spin.

    When the car is off, presumably the A/C amplifier doesn't send pulses.

    I'd assume it's most likely that the control circuitry inside the blower motor has failed, and now it just continues to run even when the A/C amplifier isn't sending it control pulses.

    On the other hand, it might be fun to scope that blue wire with the car off; perhaps it could also be that the A/C amplifier is misbehaving, and sending control pulses when it shouldn't be.

    Edit: nuts, I was hoping to get an answer on the board before somebody jumped in with checking the 12 volt battery.

    Then again, you probably do want to check the battery anyway, if it's been running this blower overnight. :D
     
    BigFatGuy likes this.
  4. BigFatGuy

    BigFatGuy Member

    Joined:
    Mar 11, 2011
    50
    42
    0
    Location:
    Oklahoma City
    Vehicle:
    2007 Prius
    Model:
    N/A
    Thanks to you both. 12V is about 6 - 8 months old, after we started getting signs of failure there.
    Is there no blower control module? Is there a way the A/C relay could have failed?
    Or is it likely that the 12V battery or blower motor, both less than a year old, has again failed?
     
  5. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    In your first post, you mentioned a blower motor resistor, but no Prius ever had one of those. In the first couple of generations, there was a separate module (active electronics, not a resistor) that would take the desired-speed signal from the A/C amplifier and convert it to driving voltage for the blower.

    As you can see in the Gen 3 diagram, that is just built into the blower motor now. It has a connection to battery (always on), and to ground, and to the blue SI signal from the A/C amplifier, telling it how fast to spin.

    So there's a couple possibilities here. One, the A/C amplifier is ok, it is not sending pulses when the car is off, but the blower motor electronics have a problem and now run at some nonzero speed even when not receiving pulses.

    Two, the blower motor might be ok, but the A/C amplifier for some reason is sending pulses even when the car is off.

    You should of course make sure the battery voltage is reasonable before trying to distinguish possibility one from possibility two.

    Simply scoping that blue wire when the car is off but the blower is running should give all the information needed to pick one of the two.
     
    BigFatGuy likes this.
  6. BigFatGuy

    BigFatGuy Member

    Joined:
    Mar 11, 2011
    50
    42
    0
    Location:
    Oklahoma City
    Vehicle:
    2007 Prius
    Model:
    N/A
    I don't have an oscilloscope, so this sounds like a dealer fix. :/
    Although they are ~$100 on Amazon.....
     
  7. tankyuong

    tankyuong Senior Member

    Joined:
    Nov 9, 2012
    1,555
    659
    0
    Location:
    Central MO
    Vehicle:
    2012 Prius c
    Model:
    II
    I would check the battery anyway cause everything is made cheap nowadays
     
    BigFatGuy likes this.
  8. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Pretty much anything that would show you there are or aren't pulses happening on that wire I think would do the trick. This is not going to be the kind of diagnosis that hinges on nuances of the wave shape. :)
     
  9. Maarten28

    Maarten28 Active Member

    Joined:
    Jul 13, 2014
    414
    222
    1
    Location:
    Netherlands
    Vehicle:
    2011 Prius
    Model:
    Three
    The Prius has the option of running the A/C while the car is off.
     
  10. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    When you activate the remote A/C feature, the car actually turns on (that's why there are warnings in the owners' manual that the wipers, headlights, etc. might come on too); it has to, because the A/C compressor itself is powered by high voltage from the traction battery, which is isolated when the car is off. Really none of that is what @BigFatGuy described in the original post.

    BFG, where did you get the blower motor you put in back in summer 2020?
     
  11. BigFatGuy

    BigFatGuy Member

    Joined:
    Mar 11, 2011
    50
    42
    0
    Location:
    Oklahoma City
    Vehicle:
    2007 Prius
    Model:
    N/A
    Blower motor was from Rock Auto. I'm cheap.

    Fortunately, it looks to be just a weird electrical issue, hopefully a one-time thing. Plugged it back in and started the car, it was off and stayed off until turning on A/C. When powering off the car, the fan stopped. A few days later, everything seems normal. Looks like it just needed an IT reset.

    [​IMG]
     
  12. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,073
    14,982
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Doesn't sound to me like a ringing endorsement of Rock Auto for blower motors.