2003 S-10 4.3 Heat Floor/def Sometimes Comes Out Panel

OK ITS A 2003 S-10 CREW CAB 4.3 VORTEC engine . I turn on the heat to come out floor and it does for about 10 min then switches to front defoger or pannel and gets the truck hot as hell how come it does not just stay on the floor VACUME PROBLEM ?

WOW no one has had this problem ok I tought someone would have had this o - well Have a HAPPY THANKSGIVING

You're posting this in interior/exterior/appearance, for some reason.

Most people look in the Blazer Problem Diagnosis forum for help, especially with mechanical issues. In other words, no one has probably seen the post to respond to it.

Sorry my mistake thank you for telling me