Suzuki: heater stopped working, floor heat, control cable

Question
My 88 sami heater has stopped working. the floor heat still works, but the upper heater just blows cool air?? I hope it is a fuse, but I don't know!! thank you

Answer
The defroster ducting comes from the sides of the heater box, one on each side, going up to the defroster nozzles.  The only other cause of such an issue in my experience would be that the control cable would have come loose or be misadjusted.  It's relatively easy to follow the cable from the heater controls to the heater box, fool around a little and determine the problem.
scotty