If your car is equipped with an automatic climate control system, the blower motor control is mounted on top of the evaporator housing which is under the plastic drip shield at the base of the windshield in the engine compartment.
Sporadic blower fan operation is usually a sign that the brushes in your blower fan motor are worn out and need replacement. If the fan either won't run at all, and then runs sporadically at low speed or high speed during turns, thats another sign of a bad blower motor. Usually it's best to replace the motor with an OEM new unit since they all eventually wear out between 7 to 10 years depending on how much the climate control is used.