Help My Heating

Tried Again To Sort My Disco 200 Heating.blows Cold Through Mid Dash Vents.no Hot Blow On Floor Or Screen.all Linkage Looks Ok And Flap Moves.no Blown Air Over Heater Rad.temp Ok And Hot Air Comes Through When Moving.i Can See A Vacuum Type Valve Up High Under The Dash That Moves Ok When Moving Lever About From Air Con To Heat,are There Any More Of These Type Valves. Help