my blower doesn't work properly. It only works on one setting, high, but that doesn't seem very high. This is my first bronco. Is the blower moter shot? I replaced the blower switch, but the same issue continues. What about the blower resistor. I don't even know exacly what that does. Napa sells the blower moter resitor wiring plug, but not he resistor it self. Anyone have any insight?