1990 W126 560 SC

Wondering if anyone can help me diagnose this problem.
After running for a while I start to hear a high pitched squealing sound coming from under the dash towards the right side. When this happens I
have turned the blower control off, and it continues. However if I turn the car off and restart it the noise goes away. This has happened only intermittently. Any ideas as to what is causing the sound? Any help will be greatly appreciated.
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Ask the folks at mbcoupes.com
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Sounds to me an awful lot like a blower motos. If yours is original then at this age you can be expecting to replace it soon.
There are two common fialure modes with this part (which is the same on all W126 chassis, coupes or sedans) and they are 1) there's a felt pad at the bottom of the blower motor shaft. If it's completely dry then a small squirt of tranny fluid may help a lot and 2) the carbon brushes, when they are totally worn out will be gone and the metal holders will dig into the motor shaft and make this noise. There's no easy way to replace these brushes, you have to get a new blower motor. Used ones will be no better, you need a new one, they're about $120 or something like that.
The first thing you'll want to do is find out where the noise comes from though, get a philips screwdriver and undo the 4 screws that hold the upholstered kick panel in place and when it's making that noise see if you can find which bit is doing it. There is another black plastic panel between you and the guts up there, just take it out and you'll now have access to the blower motor (which is 99% of the time the problem) and related electronic modules (which I've never heard failing).
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Richard Sexton wrote:

Thanks for your response, Now here is a question...is it possible for the blower motor to be making this noise while the Climate Control is in the off position? Is there some sort of auxiliary fan in there that keeps air circulating even when the Heat/AC blower is turned off? Your insight will be greatly appreciated !
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I had the same problem with my '91 300D 2.5. It happened in cold weather conditions, and was triggered by applying the brakes. The colder the ambient temperature, the greater the likelihood that the squealing would be continuous (and painful to listen to).
The difference was that in my car's case, turning off the climate control made the noise stop.
Geoff
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