Most likely and bad blower motor resistor.
Probably the blower motor resistor is shot.
Replace heater motor resistor.
The heater motor speed resister is burned out.
There is a resistor/ circuit board near the heater motor that need to be replaced. You can get one from almost any auto parts store.
the heater resistor needs to be replaced it is mounted in the heater box next to the blower motor
try replaceing the switch that controls the low to high for heater It's gonna be the blower motor resistor (near the blower motor).
The blower motor speed resistor is burned out.
The blower motor resistor is bad and goes to high fan.
The blower motor speed resistor is burned out.
Normally when a heater blower motor only works on the High setting, it is caused by a defective Blower Motor Resistor Pack. The fix is to, Replace it. In very rare instances it can also be a defective blower motor speed control switch, but rarely.
Blower Motor Resistor is bad. 20.00 part at AZ.
It is the resistor, replace it.