Resistor or switch fan motor blower

What is your question?

My fan motor is not running for heat and air. The motor is fine and some say resistor some say switch and this place say control panel? It was running then would hesitate and slow down then speed up and when I started my truck today nothing? Could it be the resistor? I hope so that's only 100.00. How can I tell? Some say the fan would run on hi only if it is the resistor and some say that isn't true....please help