1973 Dodge Dart Sport No Heat.

if you move the lever from cold to hot and nothing happens check that the cable outer is clamped at the heater box end. if it isn't the lever just slides the outer along the inner and it doesn't open the appropriate flap in the heater box

if you have aircon box and no vacuum connected up (check as above) and then

the heater will default to warming your feet

if you want it on the screen find the vacuum pod down low closest to the kick panel
pull the actuator rod as far as it will go towards the centre of the car
put a cable tie tight around it tight up against the vacuum pod to stop it moving back

you have just forced the door open that causes the warm air that was bothering your feet to be directed up out the front of the unit into the plastic conduit up to the dash vents

if the cardboard and foil tubes are in place you should now have screen demist

Dave