Front AC stops blowing, can turn fan to high but nothing from front vents

When I first turn on the air it will blow cold and
strong from all vents, but after awhile the front
vents will stop blowing. The rear still blows
cold but nothing up front. I can cycle through
the defrost, front facing and feet options but
no air. If I turn the fan all the way up I can hear
a rumbling in the in the blower like it should
be producing a lot of air, but nothing up front.
I can power off the unit and back on, it will
work for a few minutes and then same thing.