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All of a sudden there is a loud clunking noise coming from the dash of my 2005 Ford Explorer.

Observations

  • It definitely sounds cyclical.
  • Exists only when climate control system is ON.
  • Sound diminishes in frequency and intensity as you turn the temperature dial towards cold(blue). And, vice versa, is loudest and more frequent with the dial turned all the way in the red.
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  • 2
    Check the blend door actuator.
    – CharlieRB
    Apr 7, 2017 at 14:02
  • 2
    Like @CharlieRB said ... but there is probably more than one you'd have to check. More than likely three is what I'm thinking. You could narrow this down by seeing when it makes the noise by changing the settings on the climate control. Try turning the heat all the way up, leave it there for about 10 seconds, then turn it all the way down. If you hear it then, it's probably the heat/cool door actuator. Turn the inside/outside button on off in the same manner. If there is side to side control, play with those. By doing this you can narrow down which one it is most likely.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Apr 7, 2017 at 15:23
  • Your wad of $100 bills fell in the heater duct :)
    – Mark Schultheiss
    Sep 27 at 17:31

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I have had the same problem with my car. If it is a knocking sound under the dashboard once you turn on the ignition and air is only blown in the dashboard and floor, you can change the module that controls the A/C. If that does not work it may be due to a bad mode actuator that needs to be replaced.

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Typically there are three electric actuators for the Heating, Ventilation, Air Conditioning (HVAC) system on that vehicle. An actuator looks like this:

HVAC Actuator

These actuators drive a small plastic door that manages air flow inside your vehicle. There is typically one actuator for the recirculation door (max A/C?), one (or two) for temperature blend (hot / cold) and one for mode control (Defrost, panel or floor output)

Inside that actuator is an electric motor and a gear train. The gear train is made of plastic. Sometimes things get jammed up. Plastic gears get stripped. Additionally, its possible the mate between the actuator and the plastic door gets muffed up.

The noise you are hearing is definitely an actuator gone awry. You can figure out which one by carefully making changes to the settings. An alternative means is to open the glove box, squeeze the sides, open it ALL the way down. Look inside and find each of the actuators. Actually I'm pretty sure there is at least one actuator on the drivers side of the HVAC unit. Place your hand on each until you find which one is making the noise. Replace it. Pray that what is broken is the actuator and not a split inside HVAC case at the plastic door. Been there, done that.

The actuators are relatively inexpensive... but... in some cases you may have to remove the instrument panel to get to it. And that's a big job, not for the casual mechanic.

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