A/C Air Control Sensor (AUC Sensor)
 

Where is this part located in 2000 BMW 323i sedan?

Hi!!,

it is Lodged in the top of the Fan Shroud of either the Automatic or Manual.

It is on the passenger side, up on the top left of the shroud as you are looking down at it.

Real close to the Access Ports for the A/C Lines that sneak in by the radiator.

It has a "Spring" to it & it is removed by simply pushing it to the right, Tip-lifting it up on the right most end once it is pushed to the right & then sliding it back to the left & then lifting it up once again.

There are little Opposing "Claw" Feet that click into place.

The Sensor "Sniffs" the out-put from the cooling fan & determines the subsequent action.

They don't usually go bad, though.

Hope this Helps.