i have a 2003 s10 blazer 4x4 with manual hvac controls. im having trouble with air only blowing out the dash vents regardless of dial position.i found the vacuum chart but im not able to find the logic chart.any help would be appreaciated.thanks

 

i started replacing vacuum lines and i can now get air were it is supose to be.but under hard acceleration i seem to be loosing vacuum because air starts blowing out dash vents again.when i let off the gas air slowly returns to normal.i was wondering if the a bad check valve in the vacuum line could be causing this and also how long should the system hold vacuum when the motor is turned off?THANKS for any help