problem has occured for the past 2 weeks.
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2004 GMC Yukon Denali
Question: the air or heat only blows out of the defrost no matter what control is set on.
Answer #1pushrod December 13, 2012, 16:04Master
Vacuum leak under hood pass. side near firewall.
Answer #2Tomiko December 13, 2012, 17:03Journeyman
maybe your blend door is broken
Answer #3PARTS GUY December 14, 2012, 01:56Master
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 #4Greg's Orange Auto (8370 Answers) , Orange, CA - (714) 361-9355globalhelper December 14, 2012, 06:31Master
all three are good answers