Had the heater core replaced by a mechanic cause i didnt have the time to do the job myself. Wife went and picked up the car and heater and AC work great but its only blowing through the windshield defrost vents. Turning the vent selection dial does nothing. Pretty sure its the blend door actuator but i cant find where its located. Any help on this would be greatly appreciated. Also what else could it be if not the blend door actuator?