A/C dash vents dont blow air

[cxc0999]

Hey guys. This is my first time on this site so please excuse me if this is already a thread. So i recently put in a new engine on my 2002 GMC Yukon Xl 1500 and when i went to check everything was fine, i noticed the dash vents dont blow any air. All other vents work fine including the cold and hot air. Honestly not sure what could have happened since before doing the engine swap, everything worked great.