A/C Air Flow Problem (Center Vents)
 

The a/c unit air volume in my 1996 s420 works perfectly until you accelerate, and then the air volume from the center vents goes down. The outside right and left vents work perfectly no matter what speed. When you see the vacumn guage (fuel economy) in the dash and it's about 10-15 inches while accelerating, that's when the flow of air slows down. Also my glove compartment button on the dash doesn't work, is it vacumn operated also, and would that have anything to do with the a/c air flow. Should I be looking for a vacumn leak? Where would you suggest I start looking?

OF course vacuum loss is the problem! YOU need to see what is causing the vacuum leak(s). ON that & most gas engined cars you have a vacuum storage tank as well as a check valve to keep vacuum in the system. Also the central locking pump helps for upto 2 minutes!

IF you are a DIYer with vacuum testing ability & equiptment start under the passenger under dash area where the vacuum distributor for the a/c system is located.