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HVAC issues

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Team_Geek, Oct 10, 2021.

  1. Team_Geek

    Team_Geek Member

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    My 2010 Prius won’t blow hot air. The fan blows great with good air flow but the temp is cool (not cold). It also will not blow through the dash vents at all. Just on the floor or the defrost.

    The hvac control buttons light up and the display ‘works’. I tried cycling from full cold to full hot but the temp doesn’t change at all and just stays on the floor. Defrost button does put air on the windshield but it stays on the floor. The Mode button changes the arrows where the heat should go but doesn’t actually change air flow.

    Coolant flushed this summer and I installed a new thermostat and water pump at the same time (Aisin). Engine sits at 185* and I drove it for two hours tonight with no other issues. Both heater core hoses are same temp (hot).

    Thoughts on where I should start looking to fix? I’ve got an obdii dongle and android phone with torque pro and hybrid assistant. Not sure if either of those can help diagnose the issue.

    Thanks!
     
    #1 Team_Geek, Oct 10, 2021
  2. ChapmanF

    ChapmanF Senior Member

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    You can get trouble codes from the HVAC really quickly without fussing with a scan tool, just by holding down the AUTO and FRESH/RECIRC buttons while turning the car on. Look for two digit codes shown on the usual HVAC display.
     
    #2 ChapmanF, Oct 11, 2021
  3. Ldo

    Ldo New Member

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    Check/Change your cabin air filter. It could be clogged or with air flow direction installed wrong.
     
    #3 Ldo, Oct 11, 2021
  4. Team_Geek

    Team_Geek Member

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    Filter looks good and is installed the right way. I put the hvac into that code reading mode and see a flashing 97 along with the vent and fan icons flashing.
     
    #4 Team_Geek, Oct 11, 2021
  5. Team_Geek

    Team_Geek Member

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    #5 Team_Geek, Oct 11, 2021
  6. ChapmanF

    ChapmanF Senior Member

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    That would be DTC B1497, a communication error on the communication bus between the A/C amplifier and the servos that move the flaps to control the air temperature and direction.

    Here you can see the locations of the three servos, and the "air conditioning harness" that connects them (it also connects to the evaporator temperature sensor):

    [​IMG]

    The description has "bus" in it because of the shared wiring to all three servos. The A/C amplifier sends movement commands to the address of a particular servo. The "wire harness" is "smart", that is, there's a communications/driver IC built into each of its plugs where it connects to a servo. Each IC knows its address and ignores commands meant for another servo.

    The lower drawing shows how more wires would be needed without the bus scheme. (It even understates the case, because the real car has three servos, not two.)

    [​IMG]

    Here is a post with a video someone followed for gaining access.
     
    #6 ChapmanF, Oct 11, 2021
    Pdaddy likes this.
  7. Team_Geek

    Team_Geek Member

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    Ooh looks like fun. Good time to fix the squeak/rattle in my dash too. Thanks for the quick reply! Helpful as always :)
     
    #7 Team_Geek, Oct 11, 2021
  8. tankyuong

    tankyuong Senior Member

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    Check Freon level
     
    #8 tankyuong, Oct 11, 2021
  9. ChapmanF

    ChapmanF Senior Member

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    If you had a Prime, the Freon level really could matter for no heat, because the Prime has a heat pump. :)
     
    #9 ChapmanF, Oct 11, 2021
  10. Team_Geek

    Team_Geek Member

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    No Prime here. Just an old-school hybrid. They are very hard to find used in MN
     
    #10 Team_Geek, Oct 11, 2021
  11. Team_Geek

    Team_Geek Member

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    I found my chewed wires on the air outlet control servo harness. All three wires chewed on and the black wire finally busted off completely. The harness runs up between the firewall and the heater core. Does the core need to come out to replace this harness? I’m having troubles seeing where it drops down.
     
    #11 Team_Geek, Oct 18, 2021
  12. ChapmanF

    ChapmanF Senior Member

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    I don't know ... seems like kind of evil routing if it does.

    Are the damaged spots spliceable? Might be simpler....
     
    #12 ChapmanF, Oct 18, 2021
  13. Team_Geek

    Team_Geek Member

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    Well I made my situation worse. Working on getting everything cleaned up and I snapped the plastic shaft that runs the defrost/vent door. Broke in two places besides so I can’t even glue from the top side.
    Does anyone have instructions handy on removing the top plastic vent system? Would like to get it out without pulling the entire heater core but if that is my only option…
     
    #13 Team_Geek, Oct 19, 2021
  14. ChapmanF

    ChapmanF Senior Member

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    Surprised it was that snappable. Frustrating....
     
    #14 ChapmanF, Oct 19, 2021
  15. Team_Geek

    Team_Geek Member

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    Yeah old plastic I suppose. It was mouse poop mountain in there and I was apparently a little over zealous trying to clean up the mess.
    There was like a pound of bird seed in the headliner too. Ugh.
     
    #15 Team_Geek, Oct 19, 2021
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