Hi everyone I am a new member and if my question has been asked before please excuse me.

I have a new to me 1999 Econoline E-150 with 85K miles. Recently when the AC is running and I increase road speed the air vents shut down while the fan continues to run. When I get off the gas the floor vents open and then cloase and finally the dash vents re-open. My experience says vacuum leak, am I wrong here? Is there an easy way to find a leaky component/hose?

Thanks for all replies.

 

Listen for a high pitch whistle or sucking noise. May want to check nothing came loose from its intended location.