Blend door problems

With the heat on 'off', you could still feel air passing through the lower vent by the pedals. Is this the blend door not opening/closing and still letting air pass? If so, how is it corrected?

Normal operation: With the HVAC control in the "OFF" position, air enters through the cowl and exits through the floor registers for ventilation purposes. If the HVAC system looses vacuum, the blend doors default to the defrost mode and full heat is applied.