2004 GMC Yukon Denali Q&A
2004 GMC Yukon Denali Question: the air or heat only blows out of the defrost no matter what control is set on.
Vacuum leak under hood pass. side near firewall. - pushrod
maybe your blend door is broken - Tomiko
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. - PARTS GUY
all three are good answers - globalhelper