A few years ago, one of the motors (blend motors) in the air conditioning doors of my Range Rover broke down. I replaced it and since then, I have never had the same airflow as before. I can feel the main fan working fully and at various speeds but there is very little airflow through the ventilation doors. The car is cool inside but not as much as it used to be. What could it be and what should I do to get it back to its previous state?

Thanks