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You can check out blenddoor.com to purchase an alternate gear ($19) that the vendor claims is superior to the original gear that fails.

For my recent drivers side actuator failure, I purchased a new Dorman 604-108 actuator, opened it up, removed that gear that eventually fails and installed the blenddoor.com gear instead. Also lubricated it with the synthetic grease that comes with the gear. Although I could have just put the new gear in the old actuator, the whole actuator is cheap enough to replace.

Note that several models are sold on blenddoor.com so select the correct part. For my 2007 LT only the rebuilt kit that has a "larger gear on top of a smaller gear" will work. The aluminum gear, the white Delrin gear, and the black single gear (not "stacked") won't fit for my 2007. I don't know what year GM made the change where the gear (that fails) is pressed onto the shaft rather than manufactured as one piece.
 

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While performing the 50K-mile service on my '16 Limited this past weekend, I had to disconnect a multi-pin harness plug from the inlet air tube so I could pull the tube to get the air filter box open. Apparently disconnecting that harness plug causes the HVAC controls to forget their positions, and I was treated to some horrific actuator racket as soon as I keyed the ignition after buttoning everything back up.

TIP: Forget about the possibility of just needing to pull the "Display" fuse in the engine bay fuse box once you hear that infernal clacking sound. All pulling the fuse will do is reset all of your DIC data, such as your trip odometers, average fuel economy, etc. (Pissed me off to discover that these aren't backed up in static RAM!) The clacking sound you hear means one of the gears in an HVAC actuator has broken off a tooth. And I'll bet you even money that it's the intermediate gear that has the broken tooth. It's the weakest link in the gear train inside one of these things.

But I digress. In my case, it was the recirc actuator that failed - the one near the right A-pillar, behind and to the right of the glove box. Amazon sells a number of different replacement actuators, and the AC Delco # 15-74122 is only a few bucks more than the no-name Chinese junk, so I bought a few of those, knowing that I'll eventually need them all. The Delco actuators are also cheap Chinese junk, but hopefully not quite as junky as their no-name counterparts. (Rubbing that rabbit's foot for all it's worth. :) )

My order was delivered Monday, and I decided to replace the failed actuator yesterday after work. Holy crap! It's damned near impossible to replace that thing without pulling the whole dash apart! Specifically, it's an incredible PITA to remove and replace those 5.5mm hex head screws because they face out toward the fender! Going in, I pessimistically estimated 30 minutes to complete the replacement. It took me two hours, but, in all honesty, half of that was spent trying to locate and retrieve first one of the screws, and then the socket when they dropped down inside there.

But all's well that ends well. The new actuator found home right away as soon as I turned the key, and there's no more clacking. For now. Still, I can't help wondering when the next one will go or why Generous Motors couldn't have spent a few more pennies to make those gears out of pot metal, UHMW, or nylon instead of what looks like 3D-printed plastic.

I split the case of the old actuator open to see where the tooth was missing, and am thinking of buying a rebuild kit from blenddoor.com to replace that gear, but it's difficult to justify $17 for one gear (THIS ONE) when an entire Delco actuator is only $26 from Amazon. Sure, the gear is described as being made from "tough engineering grade plastic," whatever that is. But it's still plastic. I'd feel a lot better about a nylon or metal gear - even pot metal - for my seventeen bucks.

 
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Holy crap! It's damned near impossible to replace that thing without pulling the whole dash apart! Specifically, it's an incredible PITA to remove and replace those 5.5mm hex head screws because they face out toward the fender! Going in, I pessimistically estimated 30 minutes to complete the replacement. It took me two hours, but, in all honesty, half of that was spent trying to locate and retrieve first one of the screws, and then the socket when they dropped down inside there.
No doubt, it's a pain getting under the dash, looking up into dark, cramped space, then trying to reach into the tight places.

I have found some trick socket tools that help. Seems like, I used the flex screwdriver on the last actuator I replaced. It's super handy for stuff like this.

As for 2 hours, you must admit, working on your own car makes you realize that maybe some of those outrageous garage prices aren't really so outrageous :)

As for repairing the actuator, it's not that far fetched. Years ago, I opened one up (off my 07 SS) and saw the damage on slow moving gear(s). I was able to re-position the damaged teeth such that they were never engaged by the mating gear. It's been working fine in the car ever since :)

BTW, a 7/32" socket is pretty danged close to 5.5mm, altho I have both :)

Doug

[Edit]That pic makes me look ape-hairy :)

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No doubt, it's a pain getting under the dash, looking up into dark, cramped space, then trying to reach into the tight places.

I have found some trick socket tools that help. Seems like, I used the flex screwdriver on the last actuator I replaced. It's super handy for stuff like this.

As for 2 hours, you must admit, working on your own car makes you realize that maybe some of those outrageous garage prices aren't really so outrageous :)

As for repairing the actuator, it's not that far fetched. Years ago, I opened one up (off my 07 SS) and saw the damage on slow moving gear(s). I was able to re-position the damaged teeth such that they were never engaged by the mating gear. It's been working fine in the car ever since :)

BTW, a 7/32" socket is pretty danged close to 5.5mm, altho I have both :)

Doug
I don't think a Flex screwdriver or universal would work for that recirc actuator due to location and clearance issues. But I think a thumbwheel ratchet would have been just the ticket.

Unfortunately, despite the massive amount I've spent accumulating tools over the decades, I've never owned a thumbwheel ratchet. But after yesterday's "adventure", that is about to be rectified. Just ordered these little beauties ...

S-K 1/4-inch thumbwheel ratchet

S-K 3/8-inch thumbwheel ratchet


:D


 
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I don't think a Flex screwdriver or universal would work for that recirc actuator due to location and clearance issues. But I think a thumbwheel ratchet would have been just the ticket.
FWIW, that one is thumbwheel only, no ratchet. Altho I do have a larger, similar widget that does ratchet. Even without ratchet, it's still handy, especially when your hands are greasy.

But after yesterday's "adventure", that is about to be rectified. Just ordered these little beauties ...
<snip>

LOL!

Those S-K's look nice. A little expensive, but still affordable.

Doug

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This is a common issue. The air conditioner/heater has several damper actuators for controlling hot/cold , vent selection and inlet selection (fresh air/recirculation). When they fail, which is not uncommon, they will make an annoying popping sound. This is usually due to a stripped gear inside.

They cost around 35 dollars plus labor to replace, which often takes the job over 100 dollars.

With the ignition on, and AC fan on low, try adjusting your hot/cold knobs, one at a time, to see if the noise starts. Then try selecting recirc. Next try selecting a different vent (feet, face, defrost). The idea is to identify which control causes the noise to start. That indicates which of the 3 or 4 actuators need replacing.

With that knowledge, you should be in good shape for getting it repaired without getting ripped off.

HTH.

Doug

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So why does it happen when the car is turned off
 

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So why does it happen when the car is turned off
Probably powered off a RAP circuit. The noise should stop when you open the door.
 

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So why does it happen when the car is turned off
Not sure exactly why, but here is my theory. The HVAC controller calibrates the damper actuators by turning them on and watching for the current to surge indicating the damper has reached its travel limit. Then the controller powers the damper in the other direction until it stops, while timing how long it takes to reach the limit.

Knowing the total travel time enables the controller to calculate the position of the damper without needing expensive position sensors.

My guess is that, when the controller needs to re-learn a damper, it runs the calibration procedure when the car is off so as to not affect normal operation with passengers present.

When an actuator fails, typically the gears inside get stripped. This allows the actuator motor to keep turning after the damper has reached its limit. And this is what causes the clicking sound. Furthermore, because the motor is still turning, the current does not surge, so the controller keeps sending power. Hence the long clicking period until the controller finally gives up.

All this prompts the controller to set an error flag as a reminder to re-attempt a calibration next time the car is powered off. So another round of clicking.

Doug

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Not starts when I get in sometime one is own think it's one of the air vent flaps
Weird. I don't recall either of the ones in my car making a racket as soon as I got in the car. I had to start it before the racket began, and I think it always stopped when I opened the door to get out, but I can't swear to that.
 

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I had to change the module in my car this past summer. The on nearer the firewall behind the glove box. That's the tough one. And the tapping would start when I unlocked the car, and go on for a while after I shut it off.

NOW, I hear tapping when adjusting the heat cold or hot.....?? Where is THAT Module?!?!?!:mad:
 

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I had to change the module in my car this past summer. The on nearer the firewall behind the glove box. That's the tough one. And the tapping would start when I unlocked the car, and go on for a while after I shut it off.

NOW, I hear tapping when adjusting the heat cold or hot.....?? Where is THAT Module?!?!?!:mad:
Tony, do you have dual hvac controls (driver/pass.)? Can you tell which side of the dash is tapping? Driver temp bda is ~ above the gas pedal. Pass. temp bda is behind the left side of the glove box.
 
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