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2000 STS
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Discussion Starter #1
Hi all,

It all began when my blower motor begin working sporadically. Sometimes it worked fine, sometimes I turned the car on It didn't work at all. Knowing that the blower motor control module is a Common problem with these cars, I replaced it after checking the fuse under the rear seat of course. After replacement it still didn't work. I then tested the power coming into the module by using my voltmeter across the black and orange wires (There are three wires, black, orange, and black with the gray stripe). I do have regular battery voltage between the orange and black players. I read somewhere that by testing black gray stripe wire, you can tell whether the head unit was working or not. I believe I'm supposed to get the voltage when I turn the blower motor speed up-and-down. Is that between the black in the black with gray stripe wires? I have done this and it turns being up-and-down, I get nothing. In fact, I never get anything between the black and gray and the black wires. Does this mean the head unit/control is bad? Is there anything else in between that it could be? Thanks!
 

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'98 STS (RIP @ 206,xxx miles)
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4,854 Posts
....Knowing that the blower motor control module is a Common problem with these cars....
???? Oh really? Sounds like more Internet hearsay/misinformation to me.
....I replaced it after checking the fuse under the rear seat of course. After replacement it still didn't work.
No surprise there. The most common failure item is the Blower Motor; either the motor fails completely or the brushes wear to the point that contact with the armature is not reliable.
I then tested the power coming into the module....
Knowing the voltage into the Blower Control Module is all fine and good.
But what you really want to measure is the voltage into the Blower Motor, preferably with the blower motor connected to the Blower Control Module. I would use small sharp pins to puncture the insulation and make contact with the wires. Then clip your voltmeter to the pins.

At the blower motor wire harness; purple will be a variable DC voltage(+) and black is the return(-). Voltage reading will depend on the fan speed you select manually OR the fan speed the HVAC system commands if you select AUTO.

Leaving the Blower Motor connected during the above test provides an audible clue if the blower is responding to the changes in applied voltage.
 

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2000 STS
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Discussion Starter #3
Thanks for the great advice... I will check the voltage like you suggest tonight. If it is the blower motor, us replacement complicated? Do most replace the motor or are the brushes readily available? I will repost with my results!
 

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'98 STS (RIP @ 206,xxx miles)
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....If it is the blower motor, us replacement complicated?
I have no idea; mine never failed.
Do most replace the motor
Reading here and other Cadillac watering holes, most simply replace.
....are the brushes readily available?
Certainly brushes are available from a local independent starter/generator specialty shop, or they can tell you where to find them. IF in fact the brushes are obviously the problem, you can obtain brushes with the same pigtail and spring arrangement; then be prepared to do some shaping/trimming with a file.

We have become a throw-away society. Rebuilding motors/generators is becoming a lost art and many folks would not even attempt the job. But I would (and have).
 

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2003 STS w/BoseNav, 1993 Deville, 1985 Deville
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If it is the blower motor, us replacement complicated? Do most replace the motor or are the brushes readily available?
I recently replaced the blower motor in my 2003 STS. It was very easy. I think almost everyone who has had a bad blower motor just replaced the entire assembly.
 

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2000 STS
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Discussion Starter #6
ok, finally got around to testing everything out. Testing the voltage going into the blower motor revealed voltage jumping all over the place even without touching the blower motor control! The voltage varies from .5v-10v, very rapidly, all over the place. Maybe a bad blower control module from the junk yard? thoughts?
 

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White Diamond '03 DHS (with DTS floor shift)
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86,295 Posts
There is no control module. Speed is controlled internally with pulse width modulation. You probably need to replace the blower. Just remember, a junkyard blower will always be a crap shoot. May work for a week or forever.
 

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Discussion Starter #8
Isn't the blower control module the unit that plugs into the blower (the unit that has the sensor in the duct?)? i might not understand it, but how will 2v, 3v, etc. ever make the blower work? it seems like its not enough voltage going in so I should be looking for a problem before the blower motor? Thanks!
 

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Discussion Starter #10
so if the voltage is all over the place like that, should i look at another blower control module or the head unit?
 

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'98 STS (RIP @ 206,xxx miles)
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....i might not understand it, but how will 2v, 3v, etc. ever make the blower work?
Blower motor speed is a function of applied voltage.

With HVAC controls set to AUTO, the Blower Control Module decides what applied voltage (and therefore, blower motor speed) is intended at any given moment.

You are turning an ant hill into a continental divide mountain range. Replace the blower motor.
 

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White Diamond '03 DHS (with DTS floor shift)
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OK, I guess something has to control the blower. What I meant was that (unless I am mistaken) there is no external module that can be changed.
 

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White Diamond '03 DHS (with DTS floor shift)
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Oops! Guess I was still in the pre-200 mode. :bang2: :hide:
 

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'98 STS (RIP @ 206,xxx miles)
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Seville has been that way since 1998 and Deville since 2000.
No more vacuum lines or vacuum servos inside the cabin.
 

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White Diamond '03 DHS (with DTS floor shift)
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86,295 Posts
I know about the vacuum. I was thinking of the blowers on the firewall.
 

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2000 STS
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Discussion Starter #19
Ok, tonight I replaced the blower motor. NOTHING! What is there besides the head unit, blower control module, and the blower motor? From the junkyard down the street I've tried 2 blower control modules, another head unit, and a new blower motor. Nothing. And, yes, the fuse is good! Any help would be appreciated!

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When I put the voltmeter leads across the purple and black wires going into the blower motor, the voltage jumps around like I said before. Moving the fan speed control manually up and down makes no noticeable difference in the voltage jump. It jumps around every second like the following...
8.6,0, 7.4,0,8.1,0... Every second or so.
 
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