High pitch noise coming from AC/heating sys.
 

When the car is being heated, and only when the air is directed to the floor vents, I get this intermittent high pitch whistle. Goes away if I redirect the air away from the floor vents. Can anyone tell me what the problem is? Thanks.

What year & model car????

Maybe a C-class from 1994-2000?

High pitch noise coming from AC/heating sys.
 

So sorry. My first thread!!!:(
You guessed correctly.
It's a 1997, C230 with 39000km.
Thanks.

Most likely the a/c vacuum element for fresh air intake.

Try pressing the auto button & then at EC button. If the noise goes away with EC light on then the fresh air element is the problem.

High pitch noise coming from AC/heating sys.
 

Hi M.B. DOC. Thanks for your reply. I tried pressing the buttons as suggested, but the noise is still there. Only if the air is removed from the foot vents, would the noise disappear.

What exactly is the 'vacuum element for fresh air intake'? Maybe I can have a look at that.
Thanks again.
RA