Under the hood, if you follow the large hose from the brake booster to the upper manifold, there is a nipple on it and a smaller vacuum line. That is the vacuum that feeds the actuators for air flow choice. Ensure that is connected.
From there it runs under the passenger fender to the vacuum canister. Then into the cabin under the passenger side dash as a purple tube. Check the tube for vacuum inside. If it has vacuum and the air does not go where you desire, likely the nipples in the HVAC programmer have collapsed and the vacuum is not able to pass through. This can be remedied with some small vacuum hose and a little time.
Please let us know if you need the write up for that fix.