My 2001 GMC Yukon will not switch from defrost vents to face vents. It blows cold air through the defrost.

SOURCE: 2001durango vent only blows air through face vent and defroster.

the vent door is broke in the heater control box under dash

SOURCE: 2003 gmc Yukon 5.3 ..2WD air conditioner blows

A vacuum hose that controls the little door that switches where the air blows from is off, its gonna be a real chore the find which one and take the dash out to get to it, but you might get lucky and be able to look underneath the dash from the passenger side and actually see it, good luck

SOURCE: 2001 gmc yukon.hot air coming out the rear vents

try cheking the heater hoses located on the fire wall there are two of them if they are hard then they need to be replaced if they are soft then they are good. also chek the heater core

SOURCE: 2001 gmc yukon dual ac only ocold air coming out

I believe that this system has a dual condensor setup, my have an issue with the rear condensor, or a leak in the rear lines. Have a pressure test done on the rear setup to see if any freion is still in system.