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99 Seville STS, 08 STS4 N* 1SG F55
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Discussion Starter #1
A guy I met through the board here has a problem with his 90 SDV climate control - blower on high even with the key off and only through the defrost vents. If it was just the defrost vents I would think vacuum leak, possibly through the parking brake, but the blower on with the key out makes me think electrical. I read through as many posts as I could find on this and the prevailing recommendation seemed to be a bad BCM but I never saw a follow up saying that changing the BCM fixed it. The only difference with his symptoms and the threads here is that his CC panel display is still operating normally - in the posts here people were getting the 'd' in the CC and/or FDC display. His still goes between modes, but the fan stays on high even when the CC is set to 'off'. Opinions?
 

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White Diamond '03 DHS (with DTS floor shift)
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I am not sure, but I think the '90 had a separate blower control module. That would be my suspicion assuming that we are not talking about an afterblow feature enabled. If that is the case, the blower would run for a minute or so then shut off and come back on later for another minute. This would go on for about an hour I think.
 

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99 Seville STS, 08 STS4 N* 1SG F55
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Discussion Starter #3
I left out some of the description, maybe his words from the e-mail he sent me will shed some light:

"After 17 years of flawless operation the climate control started acting up. I noticed (while driving) that the fan speed was staying on "high" and not changing regardless of the setting on the climate control. If I turned the control to "Off" the system would go into "defrost" mode with the fan still running on high, even though the control display actually read "off".

I pulled into a convenience store to get a Coke and when I shut the car off the fan kept running. Even with the key in the off position. I unplugged the power connection at the fan motor so at least now it's not running, but I still don't know what's up with the climate control."
 

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'87 SDV
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Ranger nailed it. The blower control module has failed. It's located under the hood, just to the passenger side of center on the HVAC plenum on the firewall. It's mounted on the horizontal plane, and has two connectors running to it, one with 3 or 4 wires, the other with 2. It's held by two 7mm hex head screws. A common failure item on C-body Cadillacs.

It's a solid state device and cannot be serviced, only replaced. Very simple to do, just disconnect, unbolt, pull and replace. I had luck with a junkyard part. Any 1985-1992 DeVille or Fleetwood C-body module will interchange. If he can't get the part for awhile, just unplug the module to shut the fan off.
 

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99 Seville STS, 08 STS4 N* 1SG F55
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Discussion Starter #5
Thanks. Will try to find one tomorrow. If not I have a spare BCM we will replace to Easter egg it and see if that works.
 

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'87 SDV
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Don't waste your time with the BCM. If the fault was there you'd have a 'd' displayed in the CCP. The symptoms you describe point only to the blower control module. Best of luck!
 

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99 Seville STS, 08 STS4 N* 1SG F55
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Discussion Starter #7
Thanks - I was beginning to think that too since the CC display was working so I'll skip that step. There's a yard down the street from my house that has an 89 and a 93 Deville so I'll check there.
 

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99 Seville STS, 08 STS4 N* 1SG F55
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Discussion Starter #8
Don't waste your time with the BCM. If the fault was there you'd have a 'd' displayed in the CCP. The symptoms you describe point only to the blower control module. Best of luck!
Another happy Cadillac owner thanks to you guys on the forum :thumbsup: I stopped at a yard today and found an 89 CDV and a 90 Eldo with the same blower control module. Five minute change in the Sears parking lot and he was good to go. Thanks Ranger for the diagnosis and noahsdad for the location - that was key because I never would have found it otherwise. You guys rule :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup:
 

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White Diamond '03 DHS (with DTS floor shift)
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And now you look like a hero.:thumbsup: Glad it was an easy repair.
 

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'92 Deville
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This happened to me but I wriggled the ignition switch and the blower motor finally stopped. It did this about twice, but the wierd thing is that the oil light now comes on after turning the ignition to the off position.

About three weeks ago I had the ignition switch changed by a locksmith because the anti theft device was hosed (broken wire). Maybe the switch is the problem now, but I want to mention that this took place immediately upon startup after replacing an alternator.

Thanks,
Angel
 
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