problem has occured for the past 2 weeks.
GMC Q&AAsk Your Question
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, 19:04Master
Vacuum leak under hood pass. side near firewall.
Answer #2Tomiko December 13, 2012, 20:03Journeyman
maybe your blend door is broken
Answer #3PARTS GUY December 14, 2012, 04:56Master
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 (15380 Answers) , Orange, CA - (714) 361-9386globalhelper December 14, 2012, 09:31Master
all three are good answers