No defrost

I have heat and it blows but only out the dash heater vents. When I switch it to defrost or floor it still blows out the dash. It will switch off also tho. Any ideas?

A lot of times it is a vacuum leak that causes this, as the controls are run by vacuum. Might check under dash for loose vacuum lines, maybe even on motor. Could be the actuator under the dash too, but usually the line is leaking somewhere.