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AC output signal VEMS pin41?!

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  • AC output signal VEMS pin41?!

    Have search the net and read everything i could about the motronic pinouts regarding ac to AAN (UrS6 -95)
    But cannot seem to get it to work. In the latest version of VEMS you can control AC with a higher ref curve and such. The problem seem to be to find correct wire to get into vems. Have taken from aan pin 41 to analog output on vems to control ac but it doesent work. Don’t get correct signal...

    It looks like this information regards motronic:


    6/55-Connection to A/C Control Head -E87- G/Y - Used to shut off A/C for up to 12 seconds when throttle is opened rapidly at speeds under 7 kph and shut off A/C for up to 3 seconds when in first gear and throttle position is at 65 degrees or more (full load) Ref: VAG143.

    41/55-Signal from A/C control module -W/W - Tells the ECU whether the A/C compressor is on or off. This signal used by ECU to increase idle speed through ISV control when A/C compressor is activated (actually just maintains the idle speed when the extra load from A/C compressor is added to the system during idle)

    When messauring the w/w cable in the blue t6 socket it produces 9,5 voltage with ignition on, when adding snowflake (ac) it goes to ~9,8 V

    And the G/Y is 0V vs 3,5V when AC is off/on?!

    Is it suppose to be the pin 6 that activates ac clutch and communication to my vems ac setting? Anyone that have done this?

    Feels a little waist to change to MaxxECU just to get this working...


    See LINK for vems information regarding AC
    1995 Audi S6 - AAN (~350hp)
    2008 BMW 530xd (235hp)
    2008 Hyundai i30 - 1.6 CRDI (89hp)
    2011 KTM 990 SMR - custom tuned (120whp)

  • #2
    For what it's worth, I had some trouble understanding this function even with my MaxxECU.

    Initially I thought that Pin 41 was giving a AC clutch On/Off signal but it turns out that it is only telling when AC head unit requires more RPM for more cooling.
    When cabin temperature is close to the set value that signal will disappear which made my ECU think AC clutch was off.
    It wasn't, the load was clearly still there making the engine stumble on idle.

    I found out that if I want that function I need to splice in to the relay which controls the magnetic clutch 12v feed.
    Or simply live with the AC head units trickery and try to tune the idle to accommodate.

    Thing is now when my refrigerant is gone or too low in the system the magnetic clutch wont engage and as a consequence the idle is too high.
    Audi S2 -1994 | 480 Hp 650 Nm | FlexFuel | MaxxECU | 3" Stainless | Porsche GT3 Front Brakes
    http://www.garaget.org/?car=52877

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