Though having only one fan speed usually indicates a bad blower resistor a diligent mechanic at a repair shop will test the resistor fan switch and connections to the motor to make sure nothing.
Car heater fan only runs on high.
If it doesn t light up or you only have a high fan speed then your resistor block needs replacement since it is bypassed on high speed.
You tried turning on the ac and the different climate controls and it s the same.
It means that when it only worked on high that the resistor in the blower fan wiring went bad and the only speed the fan would run on would be a speed where no resistor was being used which is.