What is the sound like electrical pulsation behind dashboard in 1999 Silverado

Tiny
LHUTCHSN
  • MEMBER
  • 1999 CHEVROLET SILVERADO
  • 93,000 MILES
I've looked extensively online and nobody has asked about this. There is a sound like an electrical pulsation behind perhaps the glove compartment or the passenger airbag - like an electrical signal to something, in my Silverado truck. It lasts about 3-4 seconds and then goes off, only to come back again in about 30 seconds. Does anyone have any idea what it might be? I don't see any performance issues in the truck.
Tuesday, October 25th, 2011 AT 3:36 AM

8 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Blend door motor for the heat/ac system.

Common failure.

Roy
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Wednesday, October 26th, 2011 AT 7:03 PM
Tiny
THIS IS MIKE
  • MECHANIC
  • 686 POSTS
Lhutchsn posted this in an email.

The blend door motor. But if I turn off the A/C and the fan, shouldn't the sound stop then?
Thanks.
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Monday, October 31st, 2011 AT 6:56 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
This motor is activated by changing from cold to hot and the other is the motor that directs air flow. Does the air flow change when the noise occurs? If not, then it is the one for cold to hot.

Get a shop to verify it and give you a bid.

Sorry it took so long, I was working a 13 hour day yesterday.

Roy
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Monday, October 31st, 2011 AT 8:59 PM
Tiny
LHUTCHSN
  • MEMBER
  • 4 POSTS
I appreciate your help and am sorry you had such a long day. If I want to change the air flow I can and I can also go from hot to cold using the controls. Nothing changes when the noise occurs. It just makes that noise. Also, the noise continues even if the fan and the a/c are turned off. None of those motors should want to work then should they? Thanks again for your help.
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Monday, October 31st, 2011 AT 9:17 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
I actually love my job and get caught up in it very easily.

I was just thinking of something. Do you have a power antennae outside the truck? The relay is inside and can do this as well.

Roy
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Monday, October 31st, 2011 AT 11:09 PM
Tiny
LHUTCHSN
  • MEMBER
  • 4 POSTS
No I don't have a power antenna. Wish it were that simple.
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Tuesday, November 1st, 2011 AT 1:42 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Well, I am out of ideas. Sorry. I still think that it is one of the mode door motors. You need to have a shop listen to it and figure out the noise and give you a bid.

Roy
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Tuesday, November 1st, 2011 AT 1:58 AM
Tiny
LHUTCHSN
  • MEMBER
  • 4 POSTS
I'll do it. Thanks so much for your help.
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Tuesday, November 1st, 2011 AT 2:00 AM

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