I have a 98 Nl Fairlane
Now I've had the heater box out to replace all the plungers and blendor motor and all the foam around the doors
Everything works absolutely brilliant but had a long trip over weekend and noticed when you have the face vent on,under light or heavy acceleration it keeps going straight to windscreen
Even on fresh and recir makes no difference.
I've tried everything and have no vacuum leaks I've checked over it way to many times

Can anyone at all help me with this issue it would be greatly appreciated.

Hello, I think the ventilation system in your vehicle is likely controlled by a vacuum-operated blend door or actuator. If there is a vacuum leak or a problem with the vacuum lines, it can cause the airflow to default to the windscreen. Double-check all the vacuum lines and connections to ensure there are no leaks or blockages.

I think you should double-check all the vacuum lines and connections to ensure there are no leaks or blockages. Maybe that's the problem