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Thread: Vacumn cuts off A/C fans

  1. #11
    Administrator Ron's Avatar
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    Maybe try putting a check valve on the line feeding the mode switch (black)....

  2. #12
    Senior Member
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    My VIN:    03238 Grey & Black Hybrid - Auto - work in progress Former owner 10902 - Universal 93 Raffle Car

    It can't hurt, but I don't think I'm losing vacuum.

    Does the Automatic transmission consume vacuum in any way?

    I don't think I'm hitting the throttle hard enough to be activating the WOT switch for the AT, but I suppose I could unplug both WOT connectors and see if the problem goes away. It is worth noting that this is a new problem, and I did just repair my WOT switches... HMMM But I don't think I'm hitting
    the throttle that hard. Hard enough for the kick down sensor on the transmission, maybe, but I don't think I'm at wide open throttle for real.

    Is there an alternate set of electrical diagrams for the Automatic Transmission, and we are just all used to looking at the diagrams for the MT and we are missing something here? Maybe when the AT kick down triggers they have a circuit to lift power to AC including the Compressor and Cabin fans but because we are all looking at the MT wiring diagram we just aren't seeing it? Could it be that this is a "feature"?

    Tom

  3. #13
    Administrator Ron's Avatar
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    If the flap is closing, the actuator must be loosing vacuum.

    Place a check valve there to divide and conquer. If it then works correctly, the problem is the stock check valve, supply (leak), etc.
    Otherwise it is a leak in the mode switch, the actuator diaphragm, connection there, etc.

    No, the auto trans does not consume vacuum, I.E., it does not vent the vacuum supplied to it.

    Transmission wiring (and more) can be found HERE.

    ======

    ...when you open the throttle, engine vacuum will drop.
    ...turbo and super chargers kill vacuum.

    I'm betting on a weak check valve and/or leak(s).

  4. #14
    Senior Member
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    My VIN:    03238 Grey & Black Hybrid - Auto - work in progress Former owner 10902 - Universal 93 Raffle Car

    Quote Originally Posted by Ron View Post
    I'm betting on a weak check valve and/or leak(s).
    I hear you. I have a kit with another check valve and a supplemental vacuum accumulator I can install, but I pulled my check valve and it holds pretty good vacuum, and I'm getting more cycles out of the heat/vent test suggested above than the 1 published baseline. Maybe I can get the supplemental vacuum boost installed this weekend.

    Somewhat unfortunately I was having some electrical issues as well that I though was going to force me to pull the center console again, but sorted them without having to pull it so my access won't be quite as good.

    It may but I wonder if the problem is confined to automatics? Perhaps its because in a MT I would tend to downshift more than the AT does?

    Any suggestions for a good slot for a grapefruit sized additional vacuum accumulator? I'm currently eyeing space near the brake master but other suggestions are welcome.

    Tom

  5. #15
    Administrator Ron's Avatar
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    Quote Originally Posted by TTait View Post
    It may but I wonder if the problem is confined to automatics? Perhaps its because in a MT I would tend to downshift more than the AT does?
    That makes sense to me, if there is a leak... When under heavy load, say, starting up a long hill, you would shift a manual to 2nd before an AT would. When you let off of the accelerator to shift the MT, the vacuum will increase (replenishing the supply if there are leaks). Meanwhile, the AT's pedal is on/near the floor, so engine vacuum remains low. But that shouldn't matter because the flap is already in position. Once its actuator is fully engaged, the only way the flap should move is if the mode switch is changed or the vacuum at the mode switch input port drops. (Theoretically, you should be able to shut the engine off and the flap should remain in position, because of the check valve...) So it seems to me that it is not a "supply-reserve" problem (although a larger reservoir may help), but a leak. This is why I suggested putting a a check valve immediately before the mode switch input port as a test...

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