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 on December 13, 2012
Vacuum leak under hood pass. side near firewall.
ANSWER by on December 13, 2012
maybe your blend door is broken
ANSWER by on 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.
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ANSWER by on December 14, 2012
all three are good answers
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