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Discussion Starter #1
2010 model, LT I think, just got it about a week ago.

Anyway, I am pretty sure I know what it is, but just want to make sure.
There is the well-known knock under the dash. I am just about positive it is the blender actuator.
I found it stuck on vent, with the fan not sounding as powerful. Moved it to other positions, and it did not want to move. Then it suddenly moved, and would switch position; and the fan was stronger feeling.
Then, when I shut the car off, the knock came back. Pulling the display fuse stops it.
Given that the airflow didn't want to change, I am thinking it is the acdelco part 15-74123.

I just want to make sure, and would like to know, or get a link for replacement procedure. I tried looking this up, but I must not have been using the right terms, as I just found 1 for a year 2000.

Thanks
 

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I'd check Rockauto and/or Ebay Motors for the part#/price. May do a search up top. Member Klowny1969 may have a tutorial video on here. If not, might search Youtube. After you pulled and replaced the Display fuse, does the mode/vent selector work? Is the knock still present?
 

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Discussion Starter #3
Put the fuse back in, and the knock starts back up. I have a nissan titan and the same thing happens, so that's why I figure its the blender for zones.
 

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If you want to be sure, I have read you can pull open that area behind the glove box and feel by hand or via stethoscope for the vibration/sound to confirm which specific actuator it is. From the vent affect you are seeing, it does sound like the blend door though.
 

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Discussion Starter #5
Well, now I am not sure. Had to move the car this morning, so after I had watched a couple vids yesterday, I found the one of the actuators on the drivers side, and I was able to feel tapping that seemed to come from inside the housing.
 

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Discussion Starter #6
Huh, well I got the unit on the drivers side to knock, unplugged the power to it, and it stopped. So, it must be that one. Funny thing, I pulled the unit out, hooked 12v power to it and the motor moves fine, in either direction.
So, I disconnected the - bat cable, turned on ign and left it. Put the unit back in and buttoned it all up. Attached the -, and no knocking. Went for a drive and changed zones, and it operated fine. Stopped and locked doors, no knock.

Makes me wonder if the units do not so much go bad, as lose their calibration.

On a side note, I had just plugged in an allstate drivewise module. I have them in other vehicles, but there is a possibility that this module could have messed something up.

So, I am leaving the unit out, and seeing if the knock happens again. If not, I'll plug it back in, and see what happens.

Maybe I saved myself some coin.
 

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Funny thing, I pulled the unit out, hooked 12v power to it and the motor moves fine, in either direction.
<snip>
Makes me wonder if the units do not so much go bad, as lose their calibration.
There are several gears between the motor and the shaft - lots of gear reduction. In the one I tore apart, I found a stripped gear - teeth missing. I was able to re-position that gear with the bad teeth away from any mating gear. Put it back together, installed it, and it worked fine for years after.

It may be, while you had yours out and powered, you rotated the bad spot out of play. Keep in mind, the final gear only rotates like ±90°. So it's possible for a gear to have a bad spot that has now been moved to an unused section of the gear.

At least, that's my theory and I'm sticking to it :)

Doug

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Discussion Starter #8
Nope, no teeth missing. I pulled it apart to check! Everything looked in excellent shape.
 

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Nope, no teeth missing. I pulled it apart to check! Everything looked in excellent shape.
Interesting. If it's making the tapping sound, something has to be giving. So there has to be some elasticity somewhere in the stack of gears, or enough slack to let one gear slip past another without chewing the tooth off.

That is, as an electronics guy, I want to blame it on the mechanical stuff and not the electronics :)

Doug

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Most common w the 8th gen impalas & it’s the H-vac actuators that control the vent blinds. They have 99% chance of fail literally everyone I know that has 8th gen impala had or has this problem including me which is fine cheap & easy fix the actuators are located behind glove box which is easy to take off to make more room for working. Can grab the actuator from any real auto parts For reasonable price, can replicate this by turning climate to AC or heat or tuning off & on or anything that replicates it for your impala & you can see what one is bad by placing finger on each actuator if it is vibrating needs replacing. Hope this helps lmk for more info:)
 

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Discussion Starter #12
Well, so far, after pulling it out and inspecting it, and putting it back in; it's been fine. So, I had found the culprit unit, but I didn't have to replace it. No missing teeth or obvious damage. Works as it should.
 
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