'96 fan blows on floor only

Hi everyone, and thank you for reading my thread..here is the problem. My '96 econo fan will only blow on the feet, no dash air, no defrost, just on the feet. The a/c blows cold, and the cold---hot switch appears to be functioning well. I read elsewhere, that it is a possiblity, that i might have a crack in a vacuum tube or that it could be my vacuum reservoir. where is that reservoir located so that i can start to trace it back to the vacuum hose to the back of the environment controls. thanks.