99.5 CC DRW 6Spd 4WD 7.3l; ac htr fan blower only blows out of the defrost vents no matter where dial is set to (except off). Any ideas what the problem is? Thanks, Luke

 

The 'default' position for the venting control is 'defrost' if you have a vacuum leak.. But being it's 7.3,, it's equipped with a electric vacuum pump.. First thing to check would be thepump mounted on the right/passenger inner fender and verify its running..Is this truckESOF equipped? (Electronicshift on the fly 4x4) or does it have a manual transfer case?

 

The transfer case is manual.

 

how do you check to see if the vacume pump is working, can you hear it?