I'd say it is the blower motor resistor. They usually burn out due to a faulty blower motor that is drawing too much current. I'd reccomend replacing the blower motor and the blower motor resistor. The resistor is what allows you to have more speeds than "off" and "high". It's really simple how it works, the resistor restricts voltage to the motor, which makes it operate at less rpm, thus giving you speeds between "off" and "high". On "high" it does not route the power through the resistor, allowing the full 12 volts to the blower motor. Of course on "off" it doesnt route any power at all to the blower motor.
_________________________
2011 S 4X4 Night Armor 6 speed