I would take it to Jacob Black.
If the one speed it works on is high speed, it is the blower motor speed resisitor that is bad.
I would suspect the blower motor speed resister is shot.
Probably a bad blower motor resistor
It is due to pressure rising due to a bad condenser fan motor, bad capacitor, obstructing of airflowat the condenser, or a dirty condnser.
Most likely cause is a failed blower resistor.
worn blower motor
The blower motor speed resistor is burned out. The resistor is usually found close to the blower motor. Auto parts stores carry that part and it is easy to replace.
it has very high speed but no load
The blower motor speed resistor is burned out. The high speed function bypasses the resistor. The speed resistor is generally located near to the blower motor.
Bad switch? stalk bad wiper motor? bad low speed winding
Depends on the type of motor.
there is no fuse. for the high speed you have to have a working A/C motor