the problem is my ac only blows out the windshield defroster not out of the vents. cant figure out what is wrong any help with this problem would be great help. thanks in advance.

 

sounds like there's no vacuum to the diaphragm. make sure the vacuum line is connected to the intake manifold and is not broken.

 

also check for vacuum leaks behind the heater control panel in the car - sometimes the selector switch goes bad and has to be replaced.

 

For safety reasons ( to clear windshields in cooler climates) if you loose vacuum to the heater controls, it automatically defaults to defrost. So check both your control unit and your vacuum lines like the other posters have suggested.