air con noise

[amolak]

Hi,
There is a sound like (sucking air through a straw) coming virtually constantly through the centre vents. If I turn off the air con, it stops.
Does my air con need re-gasing?
Seems to be heard more at lower speeds.
Car is five years old, with 102k miles.

Thanks

Amo
W140 S280 1998

 

[Andy W]

Sounds like a vacuum hose come loose, if it was gas shortage the compressor would either not run, cycle on the pressure switch or you would hear an hissing noise from the expansion device which regulates the flow of refrigerant.