The level you set your vacuum depends on the height of your carpet. For bare floors, use the lowest or bare floor setting, for short and medium pile carpets use a medium setting and finally, for plush carpets use the highest setting. When vacuuming, there should be minimal resistance, if it is difficult to push, adjust to the next highest setting.
Please note some Berber carpets have a tendency to fuzz with wear. Repeated passes with your vacuum over the same area may aggravate this condition. Consider using the highest height setting or turning off the rotating brush for this type of carpet.