My dad told me today when he has max A/C on and accelerates, he hears something close then it blows through the defrost. Then he is up to speed and cruises, goes through the vents again. He thinks it's a vacuum issue in relation to the engine. I don't know much about the details of the system so I nodded my head and agreed. Anyone have this before?

 

vacuum check halve ($2 or less) on the vacuum hose that enters the cab for the AC controls.
Find where it enters the cab, back track towards engine until you find it.