W202 C230 HVAC Problem
 

1998 C230, 73K miles... with AC on, air flow from center dash vents frequently is redirected to foot well vents, particularly, but not always, during hard acceleration. After a few seconds, normal air flow resumes from center vents. Any ideas as to the cause?

That happens due to loss of vacuum to hold the a/c flaps open..most likely a fresh air diaphram

Either have someone test the vacuum system /// try pressing the [EC] button & see if they stay open..