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#1 |
Registered User
Join Date: May 2010
Location: Crossville, TN
Posts: 142
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Mystery Motor Noise In Dash Area On Key Off
This is probably normal, but I'd sure like to know what it is.
Whenever I turn off my '87 (no computer, no smog equip, carbed), I hear what sounds like a small electric motor run for several seconds. It sounds like it's coming from under the dash, right in front of me. Also, this is with the HVAC off, blower motor set to off. Thoughts on what this could be? |
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#2 |
Registered User
Join Date: Apr 2014
Location: Bloomington Indiana
Posts: 1,041
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Re: Mystery Motor Noise In Dash Area On Key Off
You sure there is an "OFF" on that blower motor? Law regarding trucks was that the fan always had to run on at least "LOW" to keep exhaust fumes from getting into the cab. I suspect what you think is OFF is really LOW, and you are hearing the blower winding down.
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Rich Weyand 1978 K10 RCSB DD. |
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#3 |
Registered User
Join Date: May 2010
Location: Crossville, TN
Posts: 142
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Re: Mystery Motor Noise In Dash Area On Key Off
Rich,
I'd thought about that, but I'd swear that the "mystery motor" activates after the key is off. What it sound like, is if there were a motorized door of some sort that opens with key on, then closes with key off, if that make sense. But, I know all of the various vents are vacuum actuated. That said, I never hear it when I start the truck, cold or warm. Jerry |
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#4 |
Moderator
![]() Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,951
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Re: Mystery Motor Noise In Dash Area On Key Off
Off is not off.
If you look at the wiring diagrams you'll see blower LOW is turned on with the ignition. Vacuum bleeding off from the heater control doors?
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And please let us know if and how your repairs were successful. |
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#5 |
Registered User
Join Date: Apr 2015
Location: Shenandoah Valley, Virginia
Posts: 332
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Re: Mystery Motor Noise In Dash Area On Key Off
Unplug your blower motor and see if you still hear it.
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85' GMC Sierra Classic Built 350; Weiand intake, Holley 600, Thumpr Cam Built 350 turbo with shift kit & 2500 Stall Thumpin' away |
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#6 |
Registered User
Join Date: Nov 2013
Location: Natchitoches, LA
Posts: 70
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Re: Mystery Motor Noise In Dash Area On Key Off
Blower motor on all squares that I have been in cannot be shut off. Only set to LOW.
Don't know why though. You have an 87 with a carb?? Must not be stock. CT |
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#7 |
Registered User
Join Date: Feb 2015
Location: Bonham, Texas
Posts: 241
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Re: Mystery Motor Noise In Dash Area On Key Off
You all say that, but my blower motor in my 82 does not run unless I tell it too by turning on either the AC, VENT, or HEAT.
That being said, it IS possible the P.O modified it, but i still have all my speed settings nor I have noticed any obvious changes to wiring. Judging by the way the aftermarket radio had been installed, I think I would notice. |
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#8 |
Registered User
Join Date: Aug 2010
Location: east tx
Posts: 128
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Re: Mystery Motor Noise In Dash Area On Key Off
If it sounds like something electrical, it might help to create the situation where you hear the noise, then pull individual fuses to see if one makes it go off. Should be on an always hot circuit, I would think. I think I once heard the lack of an off setting on the blower was a way to keep the hvac from getting dank and moldy, when I was trying to figure what the different settings did to the vac operated flappers.
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jjmorrse 86 C30 crewcab big dooley. 454- 400 |
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