If you're suspicious of heat getting into your AC you can disconnect the two heater hoses from your core at the firewall and loop them together with a coupler.
On your saturn this will be a hassle getting back there. I also don't know if one hose is 3/4 and the other 5/8, they like to do that to mess with people.
I find most of my cars use a blender door; I was very surprised with my mercedes when I turned the heat down it kept producing heat for a minute as the air blew over the heater core that was cooling down.