My heater/fan only works in 4 setting, not 3-2-1.

I had the same problem in 2 of my vehicles, and yes you can fix it easily and cheaply. It's the "blower motor resistor" unit. Located near the heater blower usually up under the glove box. It's a small unit with a port for the blower motor wires to plug into. Unplug the old one and plug in the new one. good luck!