'99 S70 Base, FWD, Auto -- Whistling Sound-- AC?

[E Showell]

I know the high pitched electronic whistling sound of the throttle body.

Since A/C recharge by local independent, I get a high pitched whistling for between 4 and 8 seconds (approx.) whenever I first engage A/C or when I shut off A/C.

Any ideas as to what this might be attributable (and please don't say: "The A/C system")? It is definitely not the throttle body singing.

[abscate]

My Beetle has done this for three years. High frequency stuff usually means little damage

( there actually is scientific basis for that statement)

A little resonance in the compressor as it pumps up the high pressure side, perhaps?

With your awareness skills, just monitor for change and enjoy your AC

On edit...and if I had your comprehension skills I would have caught this

whenever I first engage A/C or when I shut off A/C.

Happening on shut down too...almost certainly confirming a flow resonance somewhere , not to worry

[Clemens]

My 95 has done that for years. Still working like a charm. Just to prove abscate's statement. Also, he is a mod, hence he's always right...

[JRL]

Semi clogged Orafice tube?
Only when the AC is turned on? A clogged breather makes a non turbo whistle

[E Showell]

Breather?

[scot850]

Have you tried to use a piece of tube or a stethoscope to listen for the location on the noise? You will need the help of an able assistant to activate and deactivate the A/C.

Neil.

[BEJinFbk]

Mine has whistled on shutdown since I got it in'05.
Blows snowflakes - I have officially moved on.