check the blower switch, they are known to go bad, if there is any signs of heat damage replace it, volt ohm meter works good to test them
If it has only high speed, the blower motor resistor has to be replaced to get all speeds back.
Replace heater motor resistor.
The blower motor resistor pack is bad.
blower motor resistor is burned out
you have a bare wire touching on your blower motor
Blower fan inoperative or only works on high speed.
5.9 liter or 360 cubic inches. The high output was 235 hp.
More likely than not, the Blower Motor Resistor Pack is defective and needs replacing.
The heater motor speed resister is burned out.
Assuming you're talking about the blower motor, because the blower motor resistor is faulty, and needs to be replaced. On the high setting, it doesn't go through the resistor - on the other settings, it does.
the heater resistor needs to be replaced it is mounted in the heater box next to the blower motor
Defective Blower Motor Resistor Pack.