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355 Heater valve stepper motor testing.

Discussion in '348/355' started by Beetle, Jan 19, 2021.

  1. m.stojanovic

    m.stojanovic Formula 3
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    Miroljub Stojanovic
    No, there is no spring and the valve is rotary, not sliding. The valve is operated in both rotational direction by the AC ECU applying power in one and the opposite polarity of the motor. The ECU will disconnect the power to the motor when, according to the pot value, the valve has reached the desired amount of opening and the valve will stay there (until it is moved again by the ECU towards more open or more closed).
     
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  3. Qavion

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    #27 Qavion, Jan 21, 2021
    Last edited: Jan 21, 2021
    Well, someone must be right.

    Paul, was your statement based on observation or something you heard or read? Otherwise, that doesn't reconcile with the other two quotes.

    I can see how loss of signal (as in "potentiometer signal") only, would drive the valve closed, but without a spring, removing power to the valve would not move the valve, unless it's affected by water pressure.

    Miro, have you actually measured the voltage coming from the ECU or put a CRO on the line?
     
  4. Rifledriver

    Rifledriver Two Time F1 World Champ

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    Beetle is wrong. Every unit disconnected or sitting on the shelf should be open and they are not.
     
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  5. Beetle

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    Probably the way I wrote my post. I concur with Miro and Rifle driver.
    It makes sense to be always defrost windscreen. The ecu reads potential meter and then supplies a voltage to turn valve to open.
     
  6. Qavion

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    OK.. confusion over. Thanks.
     
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  8. Beetle

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    Probably should read my text a bit more instead of perusal hahahaha.
    I will try harder
     
  9. m.stojanovic

    m.stojanovic Formula 3
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    I had no chance to measure the voltages coming from the AC ECU as it was bad when I got the car and the water valve was inactive. I later removed both, the electric water pump and the valve (sold both last year) and plugged the heater hoses as I don't need heating in Malaysia. I tested the valve/motor operation just to see how it works. I new the motor runs at 12V as it was written on the Bosch sticker:
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    The potentiometer probably gets 5V from the AC ECU on its end pins so the voltage from the middle pin back to the ECU is varied 0-5V (probably some 0.5 - 4.5 volt due to the mechanical stops).
     
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  10. Beetle

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    Does the aircon still work Miro?.
    I'm guessing the ecu just sends the signal/voltage to the units you sold but the system still operates the AC side of the unit? The ecu doesn't need to see any response from these units?
     
  11. m.stojanovic

    m.stojanovic Formula 3
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    No issues at all as my "hand made" AC ECU now looks like this:

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    Of the original (bad) ECU, I have only kept the box and the push buttons/switches and built my own stand alone circuits for every function (except heating). Additional functions are a voltmeter (left digital display) which I can toggle to cabin temperature and radiator fans override switches (the two lit orange). One is to bypass the thermo switch and the other to bypass the PWM modules that I have inserted for each rad fan to enable their "soft start" and avoid big amps "bang" (~120-130 Amps, I guess, two fans starting at the same time) start-up current that happens in the original concept.

    I have also added micro switches to the fresh air and the air direction actuators to avoid stalling the actuator motors when they reach open or closed fresh air and fully up or fully down air direction.
     
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  13. Beetle

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    Wow just wow. great stuff
     
  14. m.stojanovic

    m.stojanovic Formula 3
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    I forgot to mention one more function that I assigned to the left "arrow up" button - momentary switch to (if needed) briefly run the fuel pumps and prime the system, i.e. until I see the fuel pressure up:
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    So, I have a "multi-function" AC ECU.
     
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  15. GTO Joe

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    So I guess the question is when will Ian post a drawing of your "revised" AC ECU? :eek:
     
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  16. Beetle

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    Just drove down to Melbourne and back today to pick up HVAC ECU. Had all 6 IC surface mount chips replaced. No more gremlins. Full system operational. Works perfectly. Very happy and worth the 9hr drive.
     

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