Blend door actuator location

Hi, all vents are working, except the demister on top. I took the fascia out. Turned key on for heater matrix could feel strong air from side/front ducts but very little from ducts that connect to demister. Is this a blend door actuator problem? Not moving the air through the vent ducts properly. Where would the actuator be located that controls the vents so I can check and replace it? Unfortunately my workshop manual has nothing on HVAC actuators? Also the cogs/cable on the heating control connected to some circular thing was working and turning fine.