Hissing from dashboard

Hi

I have a 92 Jimmy. There is a hissing noise coming from the dashboard area. Went I turn A/C on I dont feel anything copming out of the side or middle vents only the defroster and leg vent seem to be working ok.

Is this a bad blower motor or other suggestions.

Thanks

My guess would be a vaccuum leak. Your air controls are vaccuum controlled, so a line either fell off or is leaking.