Air Vents Make A *Thunk* Noise When I Turn On The Fan

[killian665]

I assume this noise I’m hearing is some sort of blend door actuating when I turn the climate control on but what exactly is it? It does it more than once like all of them are having trouble opening. It’s fine until it’s been turned off for a while then they’ll make noise again when I turn the system back on.

I also sometimes only get air out of one of the two center vents as if one of the doors failed to open entirely.

[rosakirk12]

I don’t turn the fan off but usually get a thunk when vent door opens a few minutes after start. I thinks this is normal but your flapper motors are not working all the time. That’s why I leave the fan switch on in the lowest output. I have been using this method about 10 years now.


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[killian665]

It’s not normal if they’re thunking open, it didn’t do that when it was new so something’s broken or worn out.