i have an 89 300ce,when i push the button with both arrows up/dwn at times it blows strong air from the 2 center vents and floor,other times if i change it,or put it back,it can take about 3 mins for the center vents to blow air again,and sometimes other setting are delayed,is this a vacum issue,or do i need a new control unit?,i notice when on auto,the fan blows really low then goes up higher,it appears to work fine.some times center vent wont even blow air.