Why won't air blow out my car vents but will blow out the defrost vents?

There are trap doors that open and close in the heat and air ducts , sounds like the doors are stuck shut, try working the controls back and forth,should hear a thump like sound if it opens up,allowing the heat to distrubute out the bottom part, spray the linkage from the contol to the box itself with wd40. As for oil I say 5w30 castrol syntheic blend well proven for cars with high millage, use it myself.