i have an 04 chevy single cab work truck. when i try to change my heater to the defrost all it does is blow air to the floor. and when i try to blow air to the floor it just blows out of the face vents. i was wondering if anybody might know what this could be caused from, maybe my switch is bad or something is clogged into my vents system so if any body can help thank you.

 

on my 96 chevy it was a linkage off the controler next to the gas peddel grab a flashlight and follow the linkage up and see if the top linkage is off hope this helps out