I would like to know about this issue as well. My dad's 03 Crown Vic has a similar problem. The air will randomly move from the defrost to the floor to the dash vents, but spends most of the time blowing thru the defrost. There is no black vacuum line on the passenger side of his car either.
The only vacuum lines I can see are from a switch attached to the top of the passenger rear engine compartment, a white line running forward to the front of the motor(under the plastic shroud), and another running to the top at the back of the motor, this switch also has a connection to the low pressure freon tube. | 
