Air flow from heater does not change to floor or defrost?

Answer 1

If this is an older vehicle the cable that controls the vent/def gate is broken or off. If this same gate is controled by a vacume servo or dashpot then the problem is either a leak in the vacume lines going to these accuators or faulty controllers themselves. Vacume leaks are sinister in that a bad leak far from your problem area can still cause a lot of problems simply by not allowing any vacume to build in the system