1994 Transport Vacuum leak fix?

It is getting warmer up here in dreary erie. that being said, I am using the a/c a lot more. The problem is, when I accelerate, the amount of air coming out of the vents is almost gone. This is extremely annoying and i wouldn't mind having it fixed...asap. Whats the easiest way of getting to the source here?

thanks

Just to clarify..when you accelerate, does the air change from panel vents to defrost? Or does the air just get warmer? And how hard acceleration?.
By design, defrost is the default position for air flow, and vacuum is required to change. There is a plastic vacuum reservoir located by the right strut tower, and is then plumbed into the vacuum manifold that contriols the function ( electric over vacuum, located under the PCM)
Also by design, when the throttle is depressed about 3/4 of the way or more, the PCM disengages the a/c compressor to reduce the load on the engine, give more power for acceration
Jeff