Brian,

It DOES sound like you have a vacuum line disconnected... It sounds as if the mixer doors aren't operating properly. I would take the dash cover off and check there as well as checking the check valve and canister problem. When you removed your stereo you may have knocked the vacuum line off the back of your A/C control. I would fix that first, before you look into the other problem.

Good Luck! Post back what you find...
SteveM14