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No cabin heat

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by MrZap, Sep 22, 2024.

  1. MrZap

    MrZap Junior Member

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    Vehicle:
    2012 Prius v wagon
    Model:
    Three Touring
    I'm wondering if anyone can provide a summarized troubleshooting checklist and/or a coolant diagram applicable to a 2012 Prius v with no cabin heat. I see where some of the useful diagrams that Mendel has made available in the past are no longer available so if anyone is able to pass those along, I'd be grateful.

    My wife is on a road trip withe the car at the moment in the interior of BC. Although the level may be a bit below the fill mark, it does not seem to be consuming coolant at an accelerated rate. I haven't got any precise info yet on where the level is relative to the markings. Now that she knows what to look for, I will post once she checks.

    The AC does work.
     
    #1 MrZap, Sep 22, 2024
  2. MAX2

    MAX2 Member

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    The first thing to check is the coolant level.
    Check the damper on the outlets, it should be in the open position.
    When you turn on the heating on the windshield and the engine is warm, is it possible to get hot air blowing?
    When the high temperature is set on the air conditioner control panel, check how the air temperature from the outlets in the cabin increases.
     
    #2 MAX2, Sep 23, 2024
  3. MrZap

    MrZap Junior Member

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    Vehicle:
    2012 Prius v wagon
    Model:
    Three Touring
    She checked coolant level and it seems to be about 3cm below the seam in the reservoir which she says is at the fill mark. She didn’t send a good photo of the full and fill marks as they seem to be behind the ac hoses from what I can tell. She’s going to get some fluid and add it tomorrow. Hopefully it’s just lack of maintenance and it’s not leaving the car somehow as that could get expensive.

    I’m concerned that I may be fooling myself but is it normal to see some loss of coolant over time? Possibly a long time.
     
    #3 MrZap, Sep 23, 2024
    Last edited: Sep 23, 2024
  4. MAX2

    MAX2 Member

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    #4 MAX2, Sep 23, 2024
  5. rjparker

    rjparker Tu Humilde Sirviente

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    Vehicle:
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    Three reasons for no heater without water pump failure / engine overheating:

    1. Air mix damper servo or linkage fail. Most likely.

    2. HG fail with coolant loss combined with resultant air (combustion gas) bubbles

    3. Clogged heater due to hgsealer

    Verify flow through heater with output from top heater hose. There is no valve in this flowpath. It will get hot quickly with the engine running (maintenance/inspection mode ideally).

    Flow is water pump through engine, out of engine to bottom heater hose, through heater core, returns via heater top hose to egr cooler and out of egr cooler to thermostat bypass port.

    Verify Air Mix damper operation with Techstream. You should be able to hear it move. Air mix damper is servo driven and is C and D in pics.

    Heater Air Mix Door in assy.jpeg Air Mix Function.jpeg Air Mix Target Pulses.jpeg
    The exhaust heat recirc heat exchanger downstream of the cats is effectively in parallel to the egr cooler. As a result it is not essential to heater operation.
     
    #5 rjparker, Sep 23, 2024
    Last edited: Sep 23, 2024
    Brian1954 likes this.
  6. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Best to get Toyota Super Long Life coolant; dealerships will have.

    what’s the miles, erm kilometres?
     
    #6 Mendel Leisk, Sep 23, 2024
  7. MrZap

    MrZap Junior Member

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    Location:
    British Columbia
    Vehicle:
    2012 Prius v wagon
    Model:
    Three Touring
    Just under 300,000km.
    No heat after topping up coolant. Shouldn't be any head gasket repair crud. Engine not overheating.
    We will follow rjparkers suggestions. Any comments on checking mixing valve without techstream? I have it at home but I won't be there for a while. Can we just set temp low then high? Is the action visible in any way. I don't even know where its located.
    Comments on repairing the mixing valve if it turns out to be that? Is this a rip the dash apart deal?
     
    #7 MrZap, Sep 24, 2024
  8. rjparker

    rjparker Tu Humilde Sirviente

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    The air mix damper is in the dash and would require major disassembly to replace it.

    Some have found disconnected linkage and have managed to connect it from under the dash one way or another.

    You might be able to hear it with the blower motor on low and simply use the temperature controls.

    I would certainly check for coolant flow at the heater hose first. A Hail Mary might flush the heater core by itself. None of this is real easy to access. Probably would need the whole wiper assembly and cowl removed.

    My guess is the air mix damper.
     
    #8 rjparker, Sep 24, 2024
    Last edited: Sep 24, 2024
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