Air only comes the defroster not out the dash no a/c

Most heater and A/C controls are vacuum operated. I would check to see if a vacuum hose fell off the unit or see something is blocking the line preventing operation of the controls.

There is a problem at the control switch. Take it off and the problem should be visible. Either the control arm on the switch has come off, or if controlled by vaccum, the hose has come off, or it may just need a new switch. Either case its in the switch. Hope it helps.