Resistors control the speed of the AC/Heater fan. These resistors are switched on and off in various combinations to create the different fan speeds. When the resistors burn out your fan will only work on the "HI" setting. The "HI" setting doesn't use any of the resistors and that's why it works. These resistors are near the blower and the blower is beneath the dashboard on the pasenger side. Just have to located resistors now.
The fan control module in the engine compartment has gone bad.
try replacing the blower motor resistor
Defective Heater Resistor Pack.
Check the low speed relay and the resistor at the motor
You most like have a bad blower motor resister.......
Heater is not working in a 2002 ford foucs only work when fan setting is place in?
try replaceing the switch that controls the low to high for heater It's gonna be the blower motor resistor (near the blower motor).
Defective heater resistor pack.
from what i have read it is the blower motor resistor it goes bad and only lets the fan run on high google blower motor resistor and read on
heater resister is bad
There is a resistor pack operated by the fan switch. It has failed. You need to replace it.
The most common cause is a failed blower motor resistor.