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Blend Door Recalibrate?

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Pyro da Cat, Aug 13, 2021.

  1. Pyro da Cat

    Pyro da Cat New Member

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    Search feature was down, so I'm posting new. If answered, can you link old Post?

    2012 C, when selecting defrost for windshield, controls work. When deselecting, hot air continues no matter what is selected. Summer failures can be brutal.

    Replaced old control panel in cabin/dash many months ago because of this problem, and broken buttons. Maybe haven't used defrost since then?! Somehow, it reset during the control panel change. Had been fine (without selecting defrost) However, this did not solve the issue because we defrosted in Los Angeles yesterday morning, then had to drive home to the desert with the heat cooking us. All other functions worked fine (temp, fan, vent mode, recirc). But now nothing works (temp, mode, esp!). Recirc and a/c might work, but hard to tell since it's so hot.

    I heard it might be possible to "recalibrate" this. Also might be required after a 12v battery change? I did replace the 12v battery a year ago... But again, here in the desert, don't need the defrost feature enough to associate the fail to battery replacement.

    Please help!! We can't drive in the heat, with the heat on!!
     
  2. Pyro da Cat

    Pyro da Cat New Member

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    Update:

    Search feature restored. Found a post about the blend door servo by redmotomaster from a couple years ago. Same description as mine.
    A/C cold when on, but when ICE comes on... Hot blast to face. I disassembled the dash, pulled the door blend servo, disassembled that and checked the servo motor itself. Works fine.

    I am at a loss now, and could use some suggestions. I don't understand HOW this is happening. A/C on, but then internal combustion engine somehow changes the blend setting all of a sudden? What program or circuit would be doing this and why?

    My guesses as to your suggestions will be:
    Get code reader, post codes
    Verify Compressor is working (it makes cold, so yes, at least a little)
    No replies, and I will submit to going to Service Dept... I will hide several notes and random items in the dash for the techs to find though, and then play dumb. ("Sir, did you know you had an abacus behind the speedometer? Duh, That's how the car converts to KPH!!)

    Lastly, are there assembly manuals that show the timing positions for the servos and doors? I marked mine and feel confident, but that would have made me feel better? $800 through Toyota.kahm with a commercial license? Lol...I'll buy a set while I am there with my 2012.
     
  3. bisco

    bisco cookie crumbler

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    i think the service manual is available by subscription for 20 bucks a day
     
  4. ChapmanF

    ChapmanF Senior Member

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    What the blend, or air mix, door does is direct some of the airflow through the heater core, and some of the airflow around it. When you want very cool air, it sends all the flow around the core. When you want very warm air, it sends all the flow through the core.

    The core is only supplied with hot coolant when the engine runs. (If the controller knows you want heat, it can keep the water pump running when the engine stops, so hot coolant continues to flow. But if it doesn't think you want heat, it won't do that, and the hot coolant will flow only when the engine runs.)

    So your symptom doesn't need "internal combustion engine somehow changes the blend setting all of a sudden?".

    All it needs is for the door to be remaining in the airflow-through-heater-core position all the time. Whenever the engine runs, that will make the air hot.
     
  5. Pyro da Cat

    Pyro da Cat New Member

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    Thank you. My confusion still remains with... Why cool air when EV, then when ICE comes on... Hot (heated) air blasts out even with A/C cold? I'm sitting in the car right now with the dash apart, cycling everything...

     
  6. ChapmanF

    ChapmanF Senior Member

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    There is a "heater core" inside that unit, and whenever the engine runs, engine coolant (which is hot) is pumped through that core.

    The whole purpose of the blend door is to direct the air flowing through the unit, either through that heater core, or around it. When working right, the blend door moves: if you ask for cool air, it blocks the heater core and sends the air around it. If you ask for heat, the door blocks the air going around the heater core, and forces it to go through. That makes the air hot.

    When you ask for heat, the controller also makes sure the engine water pump keeps running even when the engine stops, so the hot coolant keeps going through the heater core and you still get heat.

    If you're not asking for heat, there is no reason to do that, so the water pump stops whenever the engine does.

    So what do you get if the blend door is malfunctioning, and forcing the air to always go through the heater core, even when you're asking for A/C?

    In that case, in EV mode, the engine isn't running, and the malfunction doesn't matter. The A/C is cooling the air, and the air is also passing through the heater core, but who cares? The heater core isn't hot.

    Now the engine starts and hot coolant is pumped through that core, and even though the A/C is still cooling the air, it's no match for the heat being added.
     
  7. Pyro da Cat

    Pyro da Cat New Member

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    Chapman,

    Thanks! I do understand the theory of heater core. I appreciate you restating fundamentals though.

    EV mode is claiming not enough charge at the moment, so that will have to wait for now.

    I am still confused why the servo for the blender works perfectly when commanded by the temperature dial (ingnition on, not running). I watch the servo move full range. Then, start vehicle, and while in electric, A/C works good, controls match. Then ICE comes on (and like you said, starts pushing hot fluid through the heater core)...and I get heat.

    So, two possibilities:

    Blend door is getting a command to change position at ICE start OR Blend door isn't in the correct position to begin with.

    Is there a way to recalibrate the position sensor in the blend door AND has this been a problem in the past with a dead battery causing a position sensor to fail? There is a computer board in there somewhere.

    Blue skies,


     
  8. ChapmanF

    ChapmanF Senior Member

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    Maybe you could shoot and post some video of this? I might be missing something without seeing what you're seeing.
     
  9. Pyro da Cat

    Pyro da Cat New Member

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    I found another thread from last year where you commented (including diagrams) about the servo in Gen 3s as more of a digital pulse for position rather than old school open circuit type. When I had the servo apart, I was not able to access the limit switches (those coils) and am thankful that I didn't. Your explanation to the other post has helped me conclude that I need to plug this in and recalibrate the servo position. Everything mechanical checks out. Compressor, condenser, controls, servos, baffles/boxes, etc.

    I replaced the 12v battery some time ago, maybe the issue started then. We live in the desert though, so rarely use heat or defrost. Anyhow, my wife let me know about this and I have been chasing it. I tried a battery reset before and it seemed to work. In reading today, one person mentioned they had the same issue pop up AFTER they did the battery reset. To me this means they may have tricked the sensor at that moment, but the code that is stored in calibration hasn't been corrected. This is exactly what happened to us. It has been working fine and my wife is disciplined enough to not push the defrost button. I pushed it and if failed again. Since I have checked everything that moves mechanically. I am confident this is a software issue that can be resolved with the calibration through the software you mentioned. I am looking to my neighbors to see if anyone has it. Toyerta said it's $159 to plug it in and reset this. For that kind of money, and now that I am in this thing so many more hours...I am not giving up! Lol...thanks for your patience. I know it is hard to diagnose stuff here. You do a fantastic job. We live in such a great time that forums exist for pretty much everything.

    Low priority questions remain: Does the blend door have any stops on it inside the box? Does it just swivel 360? When I had the servo off to tear it apart, I checked that the blend door was not jammed. At that moment I knew I screwed up. I did not mark the position of the gear before I twisted it. So, since I was already there, I spun it around and it was free. Then I had to figure out where it used to be located so I could line up the servo correctly. The gear timing of this is predicated on the servo mechanical stop (molded into the passenger side body of the box. The servo does not move 360 when working properly. Its range is somewhere from 200-280* (from memory). There is a single gear tooth that is wide on both the servo and the gear that turns the blend door inside the box. So, what I conclude is you need to position the servo (if you have disassembled it) so the mechanical stop on the servo drive gear falls within the range of motion of the plastic stops on the box...then line up the wide tooth in the gear with the double tooth area on the servo drive gear. I found that I could move the blend door around a little with the teeth engaged and didn't even have the servo in the correct mounting position yet. But, as long as the mechanical stop on the gear is inside the stops on the box AND the special teeth line up on the blend door, it should be all good. Swiveled it into position and put the screws back in it.

    Edit: I did write notes with sharpie on several places in there. I like finding old notes when doing renovations and such...so I put my name, I put a couple stories that are hot in the news right now (Beware: COVID Lambda Variant 08/2021) and, "I'm sorry you found this...it worked when I put it together" deep in the dash on the back of a bracket, inside vent tubes..just random and fun. If you get my car and find this in 10 years, send me a message!

    Blue skies,
     
    #9 Pyro da Cat, Aug 14, 2021
    Last edited: Aug 14, 2021
  10. Pyro da Cat

    Pyro da Cat New Member

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    Broke down and went to service. Code B1441. The tech said he “pin tested” the servo and it checked out so the problem is in “the circuit.”

    I could believe that. Since I also got the same results. But my logic is flawed.

    When using the temperature dial while in EV there must be an electric heater that was producing heat. Therefore, it appeared by feel the blend door was working... however if we we add the ICE/heater core piece into the test, the blend door didn’t work. I realize now... it doesn’t work at all in any mode.

    Help me prioritize:
    New / used servo?
    New/used dash control panel?
    New amplifier (? What is that)
    Or do like grandpa would and convert the blend door to manual operation with bailing wire?
     
  11. ChapmanF

    ChapmanF Senior Member

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    The tech was probably speaking more precisely than it sounded. The Gen 3 (and c, and v) design moved some smarts into a "communication/driver IC" that is really built into the little wire harness that connects the three servos to the amplifier. There's one such IC in each of its three "bus" connectors that plug in to the servos. The servos themselves are just dumb motors, each with a pair of switches that pulse as it moves. Counting the pulses and tracking the current position is the IC's job.

    [​IMG]

    The bottom drawing is how Gen 1 and Gen 2 used to do it: each servo had a potentiometer in it that would read back the position directly as a voltage. At least it did until the potentiometer tracks got worn and the voltage skipped around, and then the amplifier would be always sending the doors back and forth trying to hold the position reading steady, and it would sound like you had mice in there, and eventually all the back-and-forth would wear the potentiometer tracks clear through.

    So the Gen 3 design eliminated that problem entirely. No potentiometer to get noisy, just simple on/off switches to make pulses. Several wires saved, and no moving parts in these ICs in the wire harness.

    And yet, there do seem to be a handful of posts where the ICs have somehow gone bad. Frustrating; they obviously worked seriously at solving the Gen 1 and 2 servo problems, and now the servos are bulletproof and the ICs flake out.

    On your list of things to change, the answer is probably "none of the above"; I'm on board with the tech in thinking it is probably that wire harness.

    B1441 is the code for failing to control the air mix damper position, no surprises there.
     
    #11 ChapmanF, Aug 19, 2021
    Last edited: Aug 19, 2021
  12. Pyro da Cat

    Pyro da Cat New Member

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    Thanks Chapman. I bought the harness and will install tomorrow. I’ll report back with results.

    Now I understand why that harness is so expensive if there are smart portions in the plugs. A few feet of wire and plastic connectors for $130...?! C’mon. But sensors and/or processors... I can appreciate that. My confidence is high that this is going to fix it. Not so much that I had a broken wire, but that in the brutal heat here, a sensor failed. Thank you thank you thank you.
     
  13. ChapmanF

    ChapmanF Senior Member

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    • Few feet of wire $1.72
    • Plastic connectors and terminals $1.06
    • 3 communication/bus driver ICs $0.45
    • Assembly and testing $7.50
    • Logistics, customs duties, warehousing, cataloging, next-morning availability to nationwide dealer network $priceless

    ... or something like that.
     
  14. Pyro da Cat

    Pyro da Cat New Member

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    Sadly, the harness did not fix it...

    Back to bad servo thoughts. I was unable to test the “limit switches“

    I think I’ll pull the servo, wire it up with power and then test continuity across the other pins to see if there is a bad coil in there... I’m bummed.

    Bonus: I’m getting faster at tearing the dash apart!!!
     
  15. ChapmanF

    ChapmanF Senior Member

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    They aren't limit switches (those would be made at the two extreme ends of travel).

    They are switches that produce a series of pulses as the servo turns. The bus IC counts the pulses, so that it can track the current position of the servo.

    With just one series of pulses, the IC would be able to tell when the servo was moving, but not which direction.

    With two series of pulses slightly offset, the motion and direction are determined.

    With a pattern that is slightly changed at one spot, motion, direction, and a known index position are determined.

    [​IMG]
     
  16. Pyro da Cat

    Pyro da Cat New Member

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    Understood, I was lazy in my reply.

    If I write this up on my bench, I should get continuity during the pulse, right?
     
  17. ChapmanF

    ChapmanF Senior Member

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    That's certainly what I would expect.
     
  18. Pyro da Cat

    Pyro da Cat New Member

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    In today's entertainment news: Dash disassembled again, servo out, bench tested and passed with no obvious issues. (See link to observe servo disassembled with pin test)

    Since I have a new harness and the blend door servo tests good... The failure is now isolated to ________???? Is there another computer/logic board/controller that would give the B1441 code?

    The blend door is free and intact. The dash controls seem to work. In EV mode, all buttons direct actions that appear normal.
     
  19. Pyro da Cat

    Pyro da Cat New Member

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  20. Pyro da Cat

    Pyro da Cat New Member

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