Most likely a bad blower resistor located to the left of the blower motor mounted to the case held in by 2 screws as the resistor coils are inside the case for cooling. You'll need to remove the knee bolster to access it and it'll come out easier if you first remove the lower right torx screw so can slightly move the dash away for clearance. I assume you have a MCC car? If so, the part's not overly expensive compared to the electronic ECC version which runs about $110. With ECC, they usually just fail completely.