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Discussion Starter #1
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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Needle probe through the wire sheathing or a back probe inserted into the backside of the harness that makes contact with the metal connector
 

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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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Discussion Starter #4
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


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?
 

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Master of the Dark Art of Diagnostics
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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.

-----------------------:yeah:
 

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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?

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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Discussion Starter #7
==============================
the blower motor controller module is shot. Period.

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

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Discussion Starter #8 (Edited)
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:

[video]https://i.ebayimg.com/images/g/Su4AAOSwCXJbJT-R/s-l1600.jpg[/video]
 

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Discussion Starter #10
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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Discussion Starter #12 (Edited)
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?
 

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

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Discussion Starter #14
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
 

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Discussion Starter #16
Common happening on GM cars with ATC in the 80s-90s. Either fail open or on full. I have a stack of them.
What component does fail on these modules?

I've showed the circuit board to an electician - he is rather sure the broken and totally burnt component was a diode. Apart from a bunch of worn soldering points everything else on the board looks just fine.

Unfortunately i do not know how to test the thyristor in the middle...
 

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As I mentioned earlier, your bad module is an aftermarket.
I have a number of good modules; some of which are the aftermarket type.
If, and I mean a big If all the aftermarket ones are the same (how many can there be); I will, if you wish, open up one and see what that burnt component is and measure it.
 

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Discussion Starter #18
As I mentioned earlier, your bad module is an aftermarket.
I have a number of good modules; some of which are the aftermarket type.
If, and I mean a big If all the aftermarket ones are the same (how many can there be); I will, if you wish, open up one and see what that burnt component is and measure it.
That would be AWESOME! I really would like to repair that bad boy :)
 

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Hey Dreffects, long time Cadillac tech here(I know, don't hate me). Check your voltage on circuit 760 with your multimeter from B+ (not ground) and back probe at module. You should have the variable 0-5v they talk about in service information when you adjust blower speed on the HVAC panel. Many techs make this mistake and the information is not all that clear. The blower motor is somewhat of a culprit in this failure. I would recommend replacing the blower motor with the new power module. Just for information, in 33 years I have never seen anything other than the module fail. I know, I said never. Very few things in this world are that sure but this is one of them.
 
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