back story - bought used in july 2020 with 169K on it at a used car lot. Prior owner(s) didn't exactly love on the car from what i can tell.

I decided to change the cabin filter - the one that was in there was beyond disgusting dirty. And i thought the engine air filter was bad when i got it. I would imagine it'd never been changed but once in the last 10 years. Of course it was all mangled like many others find.

some leaves here and there. I drove it without a filter just down the street to get a new one. Put the new one in correctly and closed it all back up. Now every single time i start it up i hear what i thought was leaves or a twig tumble around for 5-10 seconds or so and then everything is quiet - unless you put the blower/fan on high/speed 4, but that's another story.

I thought it might be leaves/debris trapped in the blower fan area and would need to vacuum it out somehow. However, i experimented and kept the blower OFF and figured now i shouldn't hear anything when i start up the car until i turn the fan back on. NOPE, the fan being on or off has nothing to do with the noise - only when i first start the car up each time, every time. And to be honest, it doesn't sound so much like the sound of leaves stuck or tumbling around as it's a sort of click/clunk sound.

Any ideas of what is making that sound?

here's what the old filter looked like...

 

I’m thinking debris in the fan, if you pull the cabin air filter out, then remove the cowl under the wiper blades, you can see down there and maybe vacuum out that debris

There it is the filter, the fan is under it.

 

Or a loose timing chain.

Or the engine was damaged from driving without an air filter.

But air does flow through the HVAC ductwork while the car is in motion set to fresh air. If the noise happens when the car is not moving, or on recirculation, with the fan off, then it's not the HVAC.

 

Mode door?

 

Is that it's technical name?

It's an actuator gear, skipping, but I don't know which "door" it's trying to sense. Mine still does it, most of the time.

 

Actually it is an actuator calibrating itself, so it knows what the state it is in. Maybe the mode door maybe the fresh air door maybe the blend door. More I think about it probably the fresh air door.

The fresh air door switches the AC, but so does the mode door.

 

i want to follow up - it turns out it is the actuator trying to calibrate itself -as donbrew describes it. It's been so long now I must be used to it as I don't always notice it when I take a drive. I had the glovebox out so i could see better to discover the noise source and can watch it open/close but when it goes in the one direction, it keeps trying to close and thus makes the clonk clonk clonk noise several times before giving up. I tried to adjust it manually with my fingers as it moved or create some resistance thinking that might get it to recalibrate. NOPE - finally gave up not wanting to break anything or make it worse... Luckily i didn't. The strange thing is how this started. All i had done was replace a very nasty old air filter from po and put in a new one. then the noise started. and yes, i changed it when the car was off.

 

Relearn procedure

https://www.chevyhhr.net/forums/prob...elector-65285/

 

what am i doing wrong?
i have radio off.
key in ignition- turn to ON but not start.
AC set to recirculate FAN on high, temp set to LOWEST cold . . . vent is on upper only - as usual in florida summer
Turn key to OFF but didn't remove from ignition
I started with just removing the big block fuse - spot 30 - then 2nd and 3rd and 4th try i removed both 10 amps in slots 10 and 16 as well since the instructions don't specify which hvac fuse to pull - there are 3 on the inside fuse panel that have HVAC in the description.
waited at least 1 min- prob 2 to be safe
replace all 3 fuses i pulled
key still in ignition- turn to ON but not start.
only hear the first cycle clonk as usual...
it always defaults to outside air when you start car and that's when you hear the noise.
when i switch back to recirc, you don't hear it clonk
i then experiment with changing air flow to blend and then to floor only
when i put it on floor only, it automatically goes back to outside air and the clonking happens again and if you try changing it to recirc while in the floor only position, it just flashes and doesn't let you do that. Thought i'd mention that in case that is a helpful clue.

 

Seems to me a dead blend door motor