heater on 1990 Buick LeSabre

hello my heater only blows out the bottom but when i put the ac on it will blow out the bottom vent's and the defrost what do i do? thanks

by in Luverne, MN on November 07, 2010
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2 answers
ANSWER by , November 23, 2010
Check the three way tee on the firewall. You will find it following the vac hose from the cruise servo check for leaks.
ANSWER by , November 07, 2010
Take a look underneath your dash for any disconnected or damaged vacuum hoses. You likely have a vacuum leak that is keeping the vacuum driven motors that turn the doors inside your dash for ventilation control from working.