AC vent actuators / mode issue

[Zelda]

All, hope I'm posting in the right place. This has to do with how my vent actuator(s)(?) are behaving. I'm pretty green to the correct nomenclature and to how things work so please bear with me.
(1997 K1500 5.7, 3 door)
I hear quick, clicking, sometimes slower and heavier sharp thumping, noises coming from the area close to where the blower motor is on the passenger side of the truck when I'm in the vehicle.
I do not believe it has to do w/ the blower motor. I think it has to do w/ how a vent actuator (if that is the correct label) is working.
The behavior is sporadic. I can get in the truck and turn the key to accessories and the clicking might start whether or not the blower fan is engaged, whether or not I've started the truck.
When I change venting modes on the air controller on the dash, in any position, I hear a rapid clicking noise. When I activate/deactivate the recirculate button, there will be a brief pause, as if the actuator is moving the "baffle" to a different position but then the clicking will resume after a few seconds (about 3-5 seconds).
Sometimes, if I depress the recirc button it will stop for a moment but then restart after a few moments. If I move it to the defrost/cabin blend mode and it is clicking rapidly and engage the recirc button after a few moments (baffle being moved?) it will turn into a slower but definitely heavier thumping noise, not a muffled sound but fairly sharp, like a slower but much louder clicking noise.
So, it varies. Mode selection, engagement of the recirc button create multiple situations. Sometimes I can start the truck and the clicking won't be present but will start in a few minutes.
With my limited knowledge I don't know if I should be looking at fuses, the control module (head unit), or the actual actuators.
Can someone familiar w/ the venting system help to clue me in to what might, well, is happening, please.
I've replaced the blower motor in the past and I know that there is a lot of plastic parts that need to be moved just to get to the working area so that is definitely ahead of me but I'm kind of flying while blind when it comes to accurate troubleshooting on this one.
I'm thinking that something is fixin' to fail. If I don't have the clicking noise to help me locate just what is clicking now, I'll be flying blind and the troubleshooting will be that much more difficult to do.
Sorry for the confusing description. I am green behind the ears, admittedly!
Thanks in advance!

 

[east302]

There are three air door actuators - one for mode (floor-dash-defrost), one for blend (hot-cold) and one for recirculation.

Mode is by the gas pedal, blend is behind the ashtray at the heater core and recirc is above and behind the blower.

The internal gears can crack, causing the sound that you’re hearing and making it unable to stay at the selected setting.

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Here is the recirc actuator viewed if you were looking through the firewall. Replacement is a bit tedious give the location, but if that’s the one making the noise then I suppose you could just unplug it if you want it to be quiet until you can replace it.

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[highwaystar]

HVAC Actuator help

Couldn't find an answer through google so I'm just wondering if anyone knows which actuator operates what? I know there is one on the driver side, one in the middle behind the climate control, and one on the passenger side, I'm currently having an issue where the air is coming out cold no matter...

www.gmt400.com

 

[Zelda]

There are three air door actuators - one for mode (floor-dash-defrost), one for blend (hot-cold) and one for recirculation.

Mode is by the gas pedal, blend is behind the ashtray at the heater core and recirc is above and behind the blower.

The internal gears can crack, causing the sound that you’re hearing and making it unable to stay at the selected setting.

You must be registered for see images attach

Here is the recirc actuator viewed if you were looking through the firewall. Replacement is a bit tedious give the location, but if that’s the one making the noise then I suppose you could just unplug it if you want it to be quiet until you can replace it.

You must be registered for see images attach

Highwaystar, that's some good info right there (and the best Deep Purple hit of all time!). Thanks for posting pictures which is going to help immensely. (Might you have posted a video on YouTube where you dove so deep into the HVAC system? I didn't bookmark the link so if it was indeed you, could you kindly post a link?) So, time to put the ear to the area to determine if it is the one behind the ash tray or the one near the blower. All signs point to the recirc actuator as I did not change the blend at all and it seems to be coming from all the way over there.
"recirc is above and behind the blower." In my mind's eye that would put that in close proximity to the glove box, IIRC. If I pulled the glove box, would I see the recirc actuator or would it be behind all that dash that is above the glove box?

 

[east302]

It’s just sort of “back there”…here’s a photo:

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[Zelda]

Thanks, hombre. Very much appreciated.

 

[Zelda]

All, I should have credited east302 for the detailed info and pics, I'm getting old and addled I guess.
Anyway, I found this video on YouTube where the feller does a pretty good job at explaining, and showing, how to tackle the recirc actuator. The comments section has some good tips on getting that top screw back in. The truck in the video is a few years older than mine, maybe the access will be a bit easier on my '97s dash.
Can't wait to pull some muscles during the contortion act of getting under the dash upside down!
Here's the link to the video:

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Highwaystar: thanks for the link to the writeup. The list of tools and procedural tips will surely help me out. Every little bit helps!