Mystery Motor Noise In Dash Area On Key Off - The 1947 - Present Chevrolet & GMC Truck Message Board Network

LuvNLife · 12-01-2015, 01:02 PM

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?

rich weyand · 12-01-2015, 04:00 PM

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.

LuvNLife · 12-01-2015, 04:14 PM

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

**hatzie** · 12-01-2015, 04:39 PM

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?

Zach079xxx · 12-01-2015, 04:40 PM

Unplug your blower motor and see if you still hear it.

nsulacountry · 12-01-2015, 05:16 PM

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

Liberty · 12-01-2015, 07:03 PM

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.

jjmorrse · 12-03-2015, 03:27 PM

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.

12-01-2015, 01:02 PM	#1
LuvNLife Registered User Join Date: May 2010 Location: Crossville, TN Posts: 142	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?

12-01-2015, 04:00 PM	#2
rich weyand Registered User Join Date: Apr 2014 Location: Bloomington Indiana Posts: 1,041	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. __________________ Rich Weyand 1978 K10 RCSB DD.

12-01-2015, 04:14 PM	#3
LuvNLife Registered User Join Date: May 2010 Location: Crossville, TN Posts: 142	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

12-01-2015, 04:39 PM	#4
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	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? __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

12-01-2015, 04:40 PM	#5
Zach079xxx Registered User Join Date: Apr 2015 Location: Shenandoah Valley, Virginia Posts: 332	Re: Mystery Motor Noise In Dash Area On Key Off Unplug your blower motor and see if you still hear it. __________________ 85' GMC Sierra Classic Built 350; Weiand intake, Holley 600, Thumpr Cam Built 350 turbo with shift kit & 2500 Stall Thumpin' away

12-01-2015, 05:16 PM	#6
nsulacountry Registered User Join Date: Nov 2013 Location: Natchitoches, LA Posts: 70	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

12-01-2015, 07:03 PM	#7
Liberty Registered User Join Date: Feb 2015 Location: Bonham, Texas Posts: 241	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.

12-03-2015, 03:27 PM	#8
jjmorrse Registered User Join Date: Aug 2010 Location: east tx Posts: 128	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. __________________ jjmorrse 86 C30 crewcab big dooley. 454- 400



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