Question about 2006 Chevrolet Silverado 2500HD 2WD

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2005 Silverado 2500HD 4WD - It appears that the pneumatic valve controlling the directional air flow from my heater/AC is getting stuck. When I switch the fan to front window defrost then back to front/bottom no air flow comes out the front or bottom air vents - the flow is entirely out the upper defrost vents. If I drive over some bumps the valve loosens and air flow again comes out the front/bottom vents. How do I fix this??? Thanks

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  • Chevrolet Master
  • 8,152 Answers

The default configuration when all vacuum fails is to defrost vents. Most likely your vacuum supply to the switch is weak. Check the connection of the supply line to the intake manifold for damage. If no problem there, trace it to the switch on the control panel. If there is an accumulator, make sure it isn't leaking and is storing vacuum. If all this is good, look at any other vacuum lines connected to the intake manifold that may be leaking and possibly reducing the vacuum supply to the HVAC control line. Let me know if you have more questions.

Posted on Sep 28, 2010

  • 2 more comments 
  • Freddy Sep 28, 2010

    I believe this vehicle does not use vacuum to direct the blend doors, these doors are driven by electrical actuators and it is one of these actuators that is going bad.

  • Jeff Turcotte
    Jeff Turcotte Sep 28, 2010

    OK, I thought they were electric on these trucks but you mentioned pneumatic. Sorry if I sent you on a wild goose chase. So there is a different troubleshooting procedure for these. Can you access the one that is getting stuck? Can you remove the actuator to see if the door is hard to move or maybe the actuator is just not working well? Hopefully it is the actuator, because it's a lot of work to fix the door. Could also be the switch, but let's start at the door.
    I will see if I can get the diagram.

  • Jeff Turcotte
    Jeff Turcotte Sep 28, 2010

    hey, I found out this isn't too bad to fix--maybe. There is an adjustment procedure. See if this makes any sense from looking at your system. I can post the pic somewhere if you need it. Unf, I can't paste it here.

    Disconnect the electrical connector to the mode actuator that is located on the left side of the air distribution case.
    Remove the screws.
    Remove the adjuster links from the control lever.
    Remove the mode actuator.
    Adjust the mode actuator by completing the following steps:
    Connect the electrical connector to the actuator.
    Turn the ignition switch to the RUN position. Allow the self-positioning of the actuator.
    Turn the ignition switch to the OFF position.
    Remove the actuator from the electrical connection.



    Fig. Blend door actuator-C/K Series


    To install:

    Install the mode actuator.
    Install the screws.
    Install the adjuster links to the control lever.
    Connect the electrical connector.
    Test the circuit operation

  • Jeff Turcotte
    Jeff Turcotte Sep 28, 2010

    I posted the pic here: http://www.fixya.com/cars/r6056118-vacuu...

    Ignore the title and everything except the last pic. Just scroll down to last pic.
    Sorry, we don't have a way to add pics after the first solution posts.

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