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Vent system problem

Tiny
JOHNR2610
  • MEMBER
  • 1993 GMC SIERRA
  • V8
  • 4WD
  • MANUAL
  • 200,000 MILES
I have a 1993 GMC 1500 and the dampers on the heating/ AC system make a thumbing sound when starting or stopping engine or switching damper positions. What causes this and more importantly how can I stop it the annoying noise? Thanks, John
Monday, January 3rd, 2011 AT 5:35 PM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Chances are one of the mode doors is sticking. All you can do is craw under the dash, locate where the sound is coming from, and from there determine what is causing it to stick. If you hear it when going from ac to heat, chances are it is the blend door next to the heater core.
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Sunday, January 9th, 2011 AT 11:41 PM

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