You most like have a bad blower motor resister.......
Defective heater resistor pack.
Check your coolant. Is it thick and gunky?
Maybe because your climate control system needs to be repaired....
the heater fan resister,it is or should be on inside or on outside heater box.
try replacing the blower motor resistor
The blower motor speed resistor is burned out.
The first thing that you need to check will be the coolant level..................
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.
Check the low speed relay and the resistor at the motor
Most likely and bad blower motor resistor.
try the bend door