2000 Chevy Lumina Airflow selector will not change

My A/C only blows out of the defrost and floor vents no matter which setting I use; it will not switch directions. This started out as an intermittent problem, but has gotten progressively worse.

I have read that this is commonly caused by a bad vacuum hose. Could someone tell me where this particular vacuum hose would be located on my car? It is a 3.1L v6 by the way.

Thanks.