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  1. #1

    Default Knocking in Heater / AC Duct

    I have a 94 Silverado, regular cab, with ac. I have just developed a rhythmic knocking in the heater / ac duct when the vehicle is started and shut off. I got down there and felt around while it was doing this and found a duct door on the far passenger side toward the bottom of the duct box and could feel it in this door. Any thoughts? Were there any service bulletins on this that anyone knows of? Thanks.

    Jim
    1994 Silverado 1500 2 wheel drive 350 TBI Auto (4L60E). Standard Cab / Bed, all power.
    Impala SS Club of America Member# 2122
    http://www.impalassforum.com



  2. #2

    Wink

    Quote Originally Posted by Poor Man View Post
    I have a 94 Silverado, regular cab, with ac. I have just developed a rhythmic knocking in the heater / ac duct when the vehicle is started and shut off. I got down there and felt around while it was doing this and found a duct door on the far passenger side toward the bottom of the duct box and could feel it in this door. Any thoughts? Were there any service bulletins on this that anyone knows of? Thanks.

    Jim
    on my sons 91 it does this it is a clicking for about ten seconds on both start up and shuting engine off , i have fugured it is the "blend acuator" if i did no kill that word he has two it is the one on the right side the hardest to get at. hope this helps

  3. #3
    Master Mechanic Silverado Junkie's Avatar
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    Feb 2010
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    Default

    Its kinda annoying. My 95 and my buddys 94 does it it.
    1995 Silverado,Z71, 3-inch lift,2-inch leveling kit, SkyJacker Suspension, short ram-air intake, throttle body spacer, MSD ignition coil, straight pipes

  4. #4

    Default

    My '05 does it too, on my mine I can slide the drivers side temp. control up one notch and it quits.
    Adam


  5. #5

    Default

    OK. I found some other information which confirmed that it is the cold air blend actuator motor. A common problem, I am finding. I was a professional mechanic in the 80's through 95 and never had to deal with this back then. I will take pics and let everyone know how it goes. Thanks for the help.

    Jim

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