the air or heat only blows out of the defrost no matter what control is set on. on 2004 GMC Yukon Denali

problem has occured for the past 2 weeks.

by in Knoxville, TN on December 13, 2012
4 answers
ANSWER by , December 13, 2012
Vacuum leak under hood pass. side near firewall.
ANSWER by , December 13, 2012
maybe your blend door is broken
ANSWER by , December 14, 2012
You have lost your vacuum to the control head. You most likely have a bad control head. Defrost is controlled by vacuum not a blend door.
ANSWER by , December 14, 2012
all three are good answers