Hissing Sound From Dashboard ??

[ToneDog]

When I start my '98 Sport I hear a hiss comming from the dash near the radio/vents when the AC/Heat is set to off, kind of sounds like a vacum leak!

Any ideas??

Thanks
ToneDog

 

[edgl]

Hissing sound from dash

There are vacuum motors under the dash, and sometimes you can hear them working. There is also a vacuum check valve to prevent the vacuum from bleeding down.

 

[tbomb]

the whistling may also be due to the fact that ford starting using plastic plenums - the whistling is the air rushing through. i have the same thing with my truck and its from the plenum, but i dont know about your truck specifically, it might be a vacuum leak, it might not.