a/c stops blowing while accelerating

In my 94 LeSabre (and also my daughter's 96 Grand Prix) the a/c stops blowing under acceleration. It used to be only heavy acceleration, but now it's pretty much any time you're not coasting. Any ideas?

Loose or corroded wire.

Actually, more accurately it doesn't "stop" blowing, it just stops coming out the vents and comes out the defrost instead. Then, when you ease off on the gas it gradually comes out the vents again, and there is a soft ticking sound (not electrical crackling, more like a door easing back into place) while the air is diverting from the defrost back to the dash vents. I don't see how a loose or corroded wire could cause this ... although of course I don't know (or I wouldn't be asking ... )

Do you have some experience with this? If so, where did you find this loose or corroded wire? Under the dash? Under the hood? Some more specifics would be much appreciated ...

To me it sounds like a problem with the vacuum control unit, which controls where the air is diverted to. This unit is located behind the glove box. On heavey acceleration the engine vacuum drops pretty much to zero and then builds up as you let off. I don't know for sure but I would think there is some kind of accumulator or check valve on the vacuum liine to stop your problem from happening.

This answer makes sense to me ... I had suspected a vacuum problem early on but my shade-tree mechanic couldn't find one ... now that I know where to look hopefully I'll locate something ... thanks!