'93 Sixty Special - Blower motor always on full speed
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, '93 Sixty Special - Blower motor always on full speed in Past Cadillac Vehicle Discussion; Hey Guys, when starting the car after a long winter the blower motor started to blow at full speed no ...
  1. #1
    DReffects's Avatar
    DReffects is offline Cadillac Owners Fanatic
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    '93 Sixty Special - Blower motor always on full speed

    Hey Guys,

    when starting the car after a long winter the blower motor started to blow at full speed no matter what is being set at the display. The blower motor runs even when it's set to 'Off'. Also I noticed a smell as if something was burnt.

    I've worked through the FSM and checked with Chart 3 "improper blower speed" and checked the voltage at the 4-pin connector to the blower motor (PIN B) for voltage. That's the pin that is supposed to provide a regulated voltage from the BCM. I don't quite know what voltage is what blower level but since I got 14.8V no matter the setting I guess that's the reason the blower motor runs at full speed.

    The next check from the FSM is supposed to be this:
    "Check Voltage from BCM Connector C1 PIN A9 to GROUND (Backprobe)"

    I do know where the BCM is located - but how am i supposed to check the voltage while the connector is not plugged in?

    Do you guys know any other location where i might get a hold of the BCM Connector or can you offer some additional insight into the issue?

    From what it looks like the error seems to be with the BCM - but I do not understand how the smell of burnt electrical parts gets from the BCM into the air vents. Each time I start the car and plug in the fuse for the blower motor I get a "fresh" breeze of that smell. So the burnt stuff should be somewhere wihtin the air vents, right?

    Thanks!

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  3. #2
    sefiro's Avatar
    sefiro is offline Cadillac Owners Enthusiast
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    Re: '93 Sixty Special - Blower motor always on full speed

    Needle probe through the wire sheathing or a back probe inserted into the backside of the harness that makes contact with the metal connector

  4. #3
    Harry Yarnell is offline Cadillac Owners Connoisseur
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    Re: '93 Sixty Special - Blower motor always on full speed

    Save yourself some grief; the blower motor controller module is shot. Period.
    Sits on top of the A/C plenum next to the blower motor.
    I've got good (tested) modules for $38 postpaid.

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    DReffects's Avatar
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    Re: '93 Sixty Special - Blower motor always on full speed

    Quote Originally Posted by sefiro View Post
    Needle probe through the wire sheathing or a back probe inserted into the backside of the harness that makes contact with the metal connector
    I was afraid of that because i do not want to damage the waterproofing.
    I'll try to get needle probes asap


    Quote Originally Posted by Harry Yarnell View Post
    Save yourself some grief; the blower motor controller module is shot. Period.
    Sits on top of the A/C plenum next to the blower motor.
    I've got good (tested) modules for $38 postpaid.
    That would explain the bad smell when the blower is activated. Are you certain? I am wondering because the disconnected 4-pin connector produced a voltage WAY OFF the diagnose sheet. In low setting it should be ~3V and I got 14.8V
    Or are those volts only measureable if the connector is connected to the blower motor controller?

    Can you ship to Germany?

  6. #5
    basscatt's Avatar
    basscatt is online now Master of the Dark Art of Diagnostics
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    Re: '93 Sixty Special - Blower motor always on full speed

    Quote Originally Posted by Harry Yarnell View Post
    Save yourself some grief; the blower motor controller module is shot. Period.
    Sits on top of the A/C plenum next to the blower motor.
    I've got good (tested) modules for $38 postpaid.
    ==============================
    the blower motor controller module is shot. Period.

    -----------------------

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    Delux68 is offline Cadillac Owners Member
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    I just bought a 93 sedan deville that seems to only blow all the way high, on every setting except low. Could that be my problem as well?

    Quote Originally Posted by Harry Yarnell View Post
    Save yourself some grief; the blower motor controller module is shot. Period.
    Sits on top of the A/C plenum next to the blower motor.
    I've got good (tested) modules for $38 postpaid.

  8. #7
    DReffects's Avatar
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    Re: '93 Sixty Special - Blower motor always on full speed

    Quote Originally Posted by basscatt View Post
    ==============================
    the blower motor controller module is shot. Period.

    -----------------------
    That's superb. Nothing makes me more happy than a confirmed error that can be fixed I'll remove the module today.

  9. #8
    DReffects's Avatar
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    Re: '93 Sixty Special - Blower motor always on full speed

    Well, you guys were absolutely right, thanks for the spot on diagnosis!
    Since my fuse housings are a wreck from the previous owner I did not even had to remove the fuse panel - just move it to the side a bit and the module came right out.

    It looks and smells burnt:


    Of course I am intersted in the root issue behind this module failing so spectacularly. Could there be a different reason besides old age for the module to go bad?

    Also, can this module be replaced by the newer version with the same connectors from a 1994 deville?

    The newer models have exactly the same connectors and overall size but a enclosed module on the back instead of an open circuitry:

    https://i.ebayimg.com/images/g/Su4AA...-R/s-l1600.jpg

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    Harry Yarnell is offline Cadillac Owners Connoisseur
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    Re: '93 Sixty Special - Blower motor always on full speed

    Yes, the module from a '94 will work.

    Fuse panel?

  11. #10
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    Re: '93 Sixty Special - Blower motor always on full speed

    Quote Originally Posted by Harry Yarnell View Post
    Yes, the module from a '94 will work.

    Fuse panel?
    Sorry, just saw that the '94 module does not look any different. I mean a module like this: Same connectors and layout but different "stuff" on the inside:


    Fuse panel:
    was this meant as a comment to the root issue behind the module failing?
    I've checked all fuses. They look fine.

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    Harry Yarnell is offline Cadillac Owners Connoisseur
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    Re: '93 Sixty Special - Blower motor always on full speed

    The '94 looks stock; your bad one is a replacement.
    If the '94 is good, then it'll work.

  13. #12
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    Re: '93 Sixty Special - Blower motor always on full speed

    Hmm I keep going back in my mind to the cause of the failure.... The diagram shows that the BCM should supply a control voltage between 0 and 5 V:



    Yet my readings at 1A9 / B (Yellow) were 14.8V when the connector was NOT connected to the Power Module.
    It also did not change when switching through the different blower speeds.

    So is it possible that the Power Module only failed due to a input control voltage that was way to high?

    Or are the 0-5V only measureable when backprobing with the connected power module?


    Edit:

    I took apart the module. Besides a few soldering points that looked rather old one major component failed in the power module: a resistor





    Behind the Gold/Gold/Green/Brown resistor is a totally wrecked other one.

    I've remove both resistors but due to the decayed state i cannot figure out what kind of resistor was sitting there.

    From the layout of the circuit board it looks like the failed resistor was directly connected to the hot 12V wire?

    All other components seem to be just fine. Does anyone know what kind of resistor goes there?

  14. #13
    sefiro's Avatar
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    Re: '93 Sixty Special - Blower motor always on full speed

    Clean and inspect the board.. Old stds would have the component spec written on the board to aid the assembler.

  15. #14
    DReffects's Avatar
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    Re: '93 Sixty Special - Blower motor always on full speed

    Quote Originally Posted by sefiro View Post
    Clean and inspect the board.. Old stds would have the component spec written on the board to aid the assembler.
    The area beneath the resistor is beyond cleaning the contacts on the rear are fine but even for the non-burnt resistor there are no markings

  16. #15
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    Re: '93 Sixty Special - Blower motor always on full speed

    Common happening on GM cars with ATC in the 80s-90s. Either fail open or on full. I have a stack of them.

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