I need help!!! I just noticed that when i drive with the air on and go over 40 miles the air suddenly changes from blowing out the panel to through the defrost vent i think i must have a vaccum leak but what do i do????

 

Yes it is a vacuum leak. You will need to list the specs on your truck so that someone can direct you to the correct forum to get exact help.

 

Hi, and Welcome to Ford-Truck Enthusiasts!
Based upon your profile, I moved your post to the 1997-2003 F150, 1997-1999 F250LD, 7700 & 2004 F150 Heritage forum from the 2009+F-150 forum.

 

Do a search on this forum.
This problem has been covered numerous times.