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Thread: HVAC temp actuator

  1. #1
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    HVAC temp actuator

    I am working on using the Fusion Brain to control the HVAC in my car. The one last thing I have left to figure out is, the temp control. I did some looking and found I should be able to use the actuator from an Audi A6 (which I just ordered)(the actuator, not the car) to allow the FB to move the temp cable. My question that I don't quite understand is...

    How do these actuators work? Do they use a timed on/off function. Like does the actuator get power for X secconds which moves the temp cable, or is it more based on voltage, (x volts out is one setting, y volts out is another). My gut says its timing, but need to know for sure, or need direction of where I can find out. lol I tried to see if I could find a schematic of the electrical etc from a 2004 A6 but didn't find much out...

  2. #2
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    It really depends on what type of actuator it is. Servos, steppers and linear actuators are commonly used. A servo would be controlled by PWM and by varying the PWM frequency to determine its position. A stepper would require a driver board and some sort of control software probably with an encoder to send back position info. A linear actuator would just use timed pulses with a limit switch at each end of the travel. If you wanted to know where the control position is, you would need some sort of encoder or at least a variable resistor.

    Does the Fusion Brain output PWM? If so, then a servo would be very easy to implement. If the actuator is a stepper, then a control board would be needed and the Fusion Brain would output one digital pulse per step (or microstep). A linear actuator would only require voltage to drive the motor and reverse polarity to reverse direction. It travels as long as voltage is applied until it reaches a limit switch.

    For the temp control, many vehicle use a dual stage control. The heat side moves a cable that opens and closes the valve to the heater core. The cold side is usually a control like a rheostat that controls when the ac compressor turns on and off.

    I'll be converting the mechanical climate controls to automatic using servos in my Montero Sport.

    How many wires does the actuator have. That might be a clue.
    Last edited by XSiveJeff; 02-07-2013 at 09:27 PM.

  3. #3
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    I don't know for sure. The part hasn't come in the mail yet. But here is the best pic I have of it...


  4. #4
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    it's listed online as a "servo", so probably uses PWM. as XSiveJeff said, when it arrives see how many pins the connector has.

    edit: found online it has 5 pins, do you have a harness for it and pinout info?

  5. #5
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    It is coming with the harness, but I don't have pinout info. I will have to look for that. Anyone know off hand where I can get that? Otherwise I will divert to google. lol

  6. #6
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    And to clarify, the FB can control stepper motors and most PWM servo's.
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    30 Digital Outputs -- Directly drive a relay
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  7. #7
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    Ok... if it is actually a servo and it has 5 wires, it is commonly known as a "dumb" servo meaning that there are no electronics inside the servo. Two of the wires will be the positive and negative power to the servo motor and 3 of the wires will be connected to a feedback potentiometer inside the case. That means that the driver board is not inside the servo. Essentially, what you have is a 12 volt gear motor with positional feedback. You can power the servo with the motor wires and reverse polarity to change direction but you will need to read the output of the potentiometer to know where it is in its range of travel. You would need some sort of control loop code to use it effectively. In a standard servo, you feed it a specific PWM frequency that relates to a specific angle or position and the internal control board determines which direction and how far to drive the motor to get it there. In the Audi, there must be a microprocessor somewhere else in the car that controls it. With that info, I will defer to someone who knows more about the Fusion Brain as far as connection and control goes.

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    Ok, its a little late now since I have the part on order, but I paid like $15 for it, so If I would be better off with a different type I am all for buying a different one. Anyone have any recommendations as to what I should get in order to make it fairly easy? I Know, I should have asked that before buying what I did. lol

  9. #9
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    Ok, I'm debating getting One of the ones at the links below. They has some schematics etc. Would these be a better options, and which one would be best, the bottom one is cheaper? And is there a way to use this information to determine what pulse speed or whatever I need to get it to work?

    http://www.bosch-ibusiness.com/boaae...5?locale=en_GB

    http://www.bosch-ibusiness.com/boaae...72/product/417
    Last edited by jjohnston; 02-12-2013 at 08:55 AM.

  10. #10
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    The first one is 24V, so you should only get that if you have a 24V system in the vehicle.

    Those are DC motors, not servos. If you want to sense position, you need one with a hall effect sensor, or some other position sensing method.
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