Power Module
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Power Module in Past Cadillac Vehicle Discussion; ...
  1. #1
    sven914 is offline Cadillac Owners Connoisseur
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    Power Module

    A few months ago, I posted a thread about my off and on blower issue. Over the summer it has gradually gotten worse, to the point where the blower in inoperable most of the time. The problem seems to be related to the outside temperature, where the blower will not work until it reaches at least 80° outside. So I found a power module today, and want to see if that will help any.

    The power module has a long black wire, which it fused to the top of the module, and then disappears somewhere behind the engine. Almost all of the modules I've seen (including the one I bought today) have a splice in that long black wire.

    I don't really want to cut out my factory power module, in case the new one is defective or the issue otherwise persists. My service manual is useless, as it just says to remove the black wire, but there's no connector, and it doesn't say where the black wire goes.

    So is there anyway to get that off, without cutting it?

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  3. #2
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Power Module

    IIRC the power module is in series with the ground connection of the blower motor. The motor is isolated from ground because of the fiberglass housing.

    That wire most likely goes to a ground connection and is probably fastened with a 10mm tin screw.

  4. #3
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Power Module

    As ape man says, there should be a 10mm hex screw on the firewall just behind the motor that holds the ground wire in place.

  5. #4
    carnut is offline Cadillac Owners Master
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    Re: Power Module

    Trace the wire to where the inner fender braces attach to the center of the firewall. Just below the passenger side brace is where that wire is grounded. But, you could ground that wire anywhere you have shinny metal to verify operation.

  6. #5
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Power Module

    Thanks... I found where it attaches to the fire wall.

    I think the power module knows I'm trying to replace it. It was about 62° degrees this morning (I park in the shade), and it came on as soon as I pressed the button.

  7. #6
    carnut is offline Cadillac Owners Master
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    Re: Power Module

    Pressed the button? I never shut mine off. I leave it at about 70 degrees all year long. The only 2 buttons I push are defrost or econ. Constantly pushing buttons wears out switches and blend door actuators. It was designed to maintain interior temp all year long, it is after all, a Cadillac! I know most people use the system like a Chevy, constantly moving temp display and changing blower speeds, thinking the system will react quicker. In the winter the blower delays till coolant temp is warm and in the summer, the fans kicks on hi to quickly cool the interior all by itself. One of the reasons I own Cadillacs is so I never turn the headlights on, need to release the parking brake or move buttons or levers to be comfortable. The first week I owned a BMW I had a dead battery because I didnt turn off the headlights! drove one block with the parking brake on! Sold it, bought another Cad.
    CADforce69 and CADforce69 like this.

  8. #7
    csbuckn is offline Cadillac Owners Master
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    Re: Power Module

    Quote Originally Posted by The Ape Man View Post
    The motor is isolated from ground because of the fiberglass housing.
    Could you get one with a metal housing to help ground it?

  9. #8
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Power Module

    Quote Originally Posted by csbuckn View Post
    Could you get one with a metal housing to help ground it?
    No, this would bypass the resistor module and the fan (which receives a constant 12V hot at all times) would run non-stop until the battery died.

  10. #9
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Power Module

    Quote Originally Posted by carnut View Post
    Pressed the button? I never shut mine off. I leave it at about 70 degrees all year long. The only 2 buttons I push are defrost or econ. Constantly pushing buttons wears out switches and blend door actuators. It was designed to maintain interior temp all year long, it is after all, a Cadillac! I know most people use the system like a Chevy, constantly moving temp display and changing blower speeds, thinking the system will react quicker. In the winter the blower delays till coolant temp is warm and in the summer, the fans kicks on hi to quickly cool the interior all by itself. One of the reasons I own Cadillacs is so I never turn the headlights on, need to release the parking brake or move buttons or levers to be comfortable. The first week I owned a BMW I had a dead battery because I didnt turn off the headlights! drove one block with the parking brake on! Sold it, bought another Cad.
    That's usually how I have mine; constantly left on at between 60 and 70°. But when this whole issue started, I found that if I turned the ECC off, before turning off the car, it would come back on latter. Now it seems to not matter what I do; as always the ECC does what ever the hell it wants.

  11. #10
    RocketFast321's Avatar
    RocketFast321 is offline Cadillac Owners Fanatic
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    Re: Power Module

    Quote Originally Posted by carnut View Post
    ! drove one block with the parking brake on! Sold it, bought another Cad.
    Ha, makes me think of this

    “I rent a lot of cars, you know, ‘cause I go on the road. I rent cars
    and when I drive a rental car, I don’t know what’s going on with it,
    right? So a lot of times I drive, like, for ten miles with the
    emergency brake on. That doesn’t say a lot for me, but it really
    doesn’t say a lot for the “emergency brake.” It’s really not an
    “emergency brake”, it’s an “emergency make-the-car-smell-funny lever.”

  12. #11
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Power Module

    Well I swapped the power module out today, and have the same problem. I haven't done a functionality test with the new module, so I don't know if it is faulty as well, but all of the lights on the head unit work and I can hear the vacuum servos moving, so it seems to work.

    I checked the ground strap again, and when I tighten it, it went past tight and now just spins in the hole. I think when I replaced the blower motor, I stripped the holes in fiberglass, so now I can't get any of the bolts past finger tight. I have an after market blower motor, and the bolts don't thread into the metal housing (I don't know if they did with the factory one), so I can't get the ground strap bolted down super tight. I am sure that after all this frustration, that is the only cause of my problem.

  13. #12
    carnut is offline Cadillac Owners Master
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    Re: Power Module

    So, run a wire with alligator clips (roach clips) on both ends from a bare metal section of the blower motor to a bare metal underhood ground. Next time use a 1/4 in. socket wrench or a nut driver to secure the motor. If necc. drill out the holes one size larger on the motor and use one size larger sheet metal screws.

  14. #13
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Power Module

    As stated above, running a ground wire from a bare metal part on the blower motor to a bare metal part on the engine bay will by-pass the resistor and the blower motor will run continuously.

  15. #14
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Power Module

    ^That's exactly what I was going to say...

    One of the things I was thinking was to drill out the holes and insert plugs that have threading on the inside of them. I know I can get something like that in brass or stainless, but I want to try and find it in PVC.

  16. #15
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Power Module

    If you do any drilling involving the fiberglass housing avoid the dust. This includes dust when the AC is first run. Nasty stuff.

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