Jeep Repair: A/C vent, jeep grand cherokee, vacuum line

Question
A/C works fine.  Blows cold but blows from defroster and heater vents.  HVAC controls seem to work.  Is this a vaccum problem?  Any suggestions?

Answer
I need to know what year make and model.  If this is a 99-05 jeep grand cherokee you need to check the vacuum line on the driver's side of the intake manifold.  They tend to swell and no longer hold in place.  On the 4.0L this hose mounts to the side facing the airbox and brake booster.  On the 4.7L this fitting is mounting just behind the throttle body on the side.

In either case the use of a zip-tie may help hold the hose in place but I have seen this eventually fail because the hose swells from heat and exposure to crank-case fumes and oil.  End result being that the hose deteriorates and the zip tie will not hold.
Doug