If the blower fan does not work on settings 1 and 2 but does work on settings 3 and 4 How do you know if the resistor pack relay fuse switch or fan motor is the problem?

check the fan connector under the dash. it should be a four prone connector, which control the fan speed. replace it and it will work. If It works at some speeds and not others it is always the resistor that is At Fault . The slowest speeds usually will go first as the have the most resistance and therefore under the most stress . High speed will always work as there is no resistance just a direct feed to the motor