problem with air condition ducts

[osama]

hello.. i have a 95 w140 600.. the best car i ever had by far.

ok.. there is a problem with the air blowing from the ducts. Whenever I accelerate the air is directed to the windshield.

the higher the economy gauge goes the more the air is directed to the windshield..the lower it goes the more the air come out the front ducts.

I am assuming here the problem is related to some vacuum line, i imagine that when more vacuum is generated in the engine , some vacuum line "suck" the "duct flap" which leads the air to to the windshield.

I live in an area where temperature is 47 c . So this is inconvenient for me.

Thank you.