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Q: AC tapping noise when on recirculation.

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I have had a recurring problem with A/C blower only working on four. I know that is due to a bad blower resistor and/ or cable. This problem goes back years. I push the buttons repeatedly or wiggle the cable and it temporarily fixes it for a few minutes or weeks. New problem is a loud tapping when a /c in recirculate mode. Takes about 5 seconds after engaging recirculation. I can put in recirc and change from dash outlet to lower heater or defrost or defrost combo and no tapping. When normal dash has to be in fresh air mode, otherwise tapping.

My car has 80000 miles.
My car has an automatic transmission.

Hey there. The tapping noise you are hearing is most likely the air circulation door actuator. There is a separate actuator for the mode door position. The mode door directs the air out the various vents on your dash and the recirculation door opens and closes a door to fresh air from the outside of your car. The noise you are hearing is very common across all manufacturers. The internal gears of the actuator are broken at the end of its travel. Eventually, this will lead to a complete failure of the actuator. If you would like a precise diagnosis of this, a certified technician, like one from YourMechanic, can inspect the tapping noise in person and proceed with repairs.

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