why does the ac blow through the defrost but not the vents on 1993 Chevrolet G Series Van (G20)

it happens every time i cut the ac on.

by in Four Oaks, NC on June 08, 2013
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1 answer
ANSWER by , June 08, 2013
Vacuum leak under hood passenger side small black hose near firewall. Also black vacuum amplifier ball may be defective!