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Thread: HVAC control for 98 GMC Savana.

  1. #1
    Maximum Bitrate stonestatue's Avatar
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    HVAC control for 98 GMC Savana.

    I have a 1998 GMC Savana that's currently in the process of having a carputer installed. One of the things I intend to do is make the HVAC controls through an interface in Digital FX. I understand Fusion Brain can make this happen.

    But I want to know exactly how and where to connect everything. This requires knowing what kind of system my HVAC is. I have some basic knowledge of how it operates (unless I'm wrong).


    I have included a picture of the control panel (taken out).

    The first dial is the fan speed control. There are four speeds that correspond to each setting on the fan speed dial. Each setting sends voltage to a respective relay each which connect to a resistor of different amounts. The blower motor requires current from the mode selector dial.

    Which leads me to the dial on the far right, the mode selector. There are eight different spots for the dial to choose. The first one is off, which opens the circuit and cuts off current. The next three are Max A/C, A/C, and Blend A/C (self titled). All three of these send a current to the A/C compressor to turn on and make cold air. I am not sure the difference between Max A/C, A/C, and Blend. I want to assume that Max A/C and A/C are different fan speeds, but there is already the fan speed dial which is separate. Next is the non A/C modes; vent (top), vent (bottom), mix (defrost/bottom), and defrost. These are determined by different vacuum lines. I have included a picture of the vacuum connections behind the control panel in my van:



    You can't really see the lines themselves, but they're behind the red circle thing. There are six lines in all. One supplies vacuum and the other five feed off the supply vacuum line, depending on which setting the dial is on. I am not sure which mode each line corresponds with, but some obviously have to overlap, since there are more setting than there are feed lines (5).



    This is a picture of two more vacuum lines that aren't part of the six others in the red circle. These plug into a separate area of the control panel. However, I did notice that the black vacuum line is spliced with the black vacuum line on the other group of vacuum lines, so I assume that they're both the supply then. I also assume that these two vacuum lines have something to do with the temperature dial, because when I turn the dial with the engine off, I can hear vacuum escaping and a blend door move inside the HVAC ducts. It bears mentioning that in the wiring schematic for the HVAC system, it shows an "Air Temp Actuator" with a logic unit inside, which is definitely electronic driven, not mechanically driven directly by a cable. I also noticed three electrical contacts behind the temperature dial. Lastly, the temperature dial has fixed "notched" turns, not just a free spinning dial. I counted 21 notches for the dial. Based on all this, I can make an educated guess that the air temperature actuator is a stand alone unit that takes electronic feedback from the temperature dial. It creates a PWM signal based on which notch the dial is on and electronically controls a blend door, but I'm not entirely sure about this part.

    So here is how I intend to interface all this:
    - The fan speed control has four wires, each of which can be connected to digital outputs which will activate the respective relay.
    - The mode selector will require electric vacuum solenoid actuators which will send vacuum to the correct vacuum line, once I determine which each one does. Also, the Max A/C, A/C, and Blend modes will send a voltage to the A/C compressor wire from the back of the control panel to mimic the control panel.
    - The temperature control will consist of 21 digital outputs, one for each electronic "notch" on the dial itself.

    I apologize for this long winded post. I just wanted to make sure I covered as much as possible in the first post so I can get this thing off the ground. All of the information above are based on my personal observations and educated guesses are nothing more than assumptions. I could be badly mistaken about any of the above. For this reason, I ask anyone and everyone that would know better to please feel free and post and correct any information/assumptions I got wrong as well as add any feedback. I do intend to scan the wiring schematic for this system once I get access to a scanner, hopefully in a few days. Thanks for your input.
    Check out my GMC Savana worklog.

    Remaining tasks to facilitate vanputer installation codename "Enterprise":
    - Edit skin to liking.
    - Get compatible phone for mobilephone.net.
    - Facilitate HVAC control.

  2. #2
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    Sorry for thread digging, But how did you go with this? I'm about to start work on my HVAC and it seems to be a near identical system.

  3. #3
    Maximum Bitrate stonestatue's Avatar
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    No problem for the thread digging. I'm just glad to get SOME response. I never did anything with it (yet). I'm still considering whether or not I want to do this, or if I just want to leave it like that.
    Check out my GMC Savana worklog.

    Remaining tasks to facilitate vanputer installation codename "Enterprise":
    - Edit skin to liking.
    - Get compatible phone for mobilephone.net.
    - Facilitate HVAC control.

  4. #4
    Maximum Bitrate stonestatue's Avatar
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    What kind of vehicle do you have?
    Check out my GMC Savana worklog.

    Remaining tasks to facilitate vanputer installation codename "Enterprise":
    - Edit skin to liking.
    - Get compatible phone for mobilephone.net.
    - Facilitate HVAC control.

  5. #5
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    I have a Holden Commodore. Or to you guys, it's a four door version of the Pontiac GTO, sort of lol.

  6. #6
    Maximum Bitrate stonestatue's Avatar
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    What is your intention?
    Check out my GMC Savana worklog.

    Remaining tasks to facilitate vanputer installation codename "Enterprise":
    - Edit skin to liking.
    - Get compatible phone for mobilephone.net.
    - Facilitate HVAC control.

  7. #7
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    World peace?...

    I'm not sure what you mean. If I understand: I intend to ditch the heater controls on my dash, extend my 'din slot' and place a 10 inch touchscreen in instead and control my heater from the touchscreen.

  8. #8
    Maximum Bitrate stonestatue's Avatar
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    Yeah, I meant what are you doing with your car, concerning the carputer.
    Check out my GMC Savana worklog.

    Remaining tasks to facilitate vanputer installation codename "Enterprise":
    - Edit skin to liking.
    - Get compatible phone for mobilephone.net.
    - Facilitate HVAC control.

  9. #9
    Maximum Bitrate stonestatue's Avatar
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    Update: I called the local Chevy dealer asking them about the temperature dial. It has 21 positions and each position sends a unique resistance to the controller, just like a rheostat. I believe the Fusion Brain can easily replicate this with just one digital output and a software defined resistance value based on which "button" I press.
    Check out my GMC Savana worklog.

    Remaining tasks to facilitate vanputer installation codename "Enterprise":
    - Edit skin to liking.
    - Get compatible phone for mobilephone.net.
    - Facilitate HVAC control.

  10. #10
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    I see your worklog first and then discover this thread you made before. This contains a lot of information which is very useful. I have the same intention to modify my HVAC as you do.
    Does the fusion brain have a interface can define resistance value? I look around at fusion brian's website but didn't see how to define resistance. Fusion brian seems can only take input from sensors and output by controlling relays.

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