faulty blower motor resistor
Probably your blower motor speed resister is burned out.
What about it? Need more info.
If the one speed it works on is high speed, it is the blower motor speed resisitor that is bad.
blower resistor is bad
Replace the high speed relay.
Only for the high speed blower function. The lower speeds go thru the blower motor speed resister.
look in owners manual for a fuse that might control motor, could be a bad motor or a bad switch, these cars are known for the multi speed resistor going bad but when it fails high speed still works
Defective blower motor resistor pack.
If you have no blower speeds at all, first check the fuse. If the fuse is okay I would suspect the blower speed switch and its electrical plug has melted. If the switch checks okay I would suspect the blower motor is bad. If you have high speed only, I would replace the blower motor speed resistor. If you have all lower blower speeds but no high speed, replace the high speed relay.
the blower fan rheostat usually located in blower box is like a resistor that draws energy from the blower fan supply to slow it down and there is a high speed fan relay for the fastest speed. So your rheostat is not working
There is a replaceable resistor which is in the engine compartment located on the blower. It is usually fastened by two small screws. Remove the electrical connectors and get a replacement. If the resistor is burned out you will still have high speed. If you have the lower speeds but no high speed, replace the blower motor high speed relay. If you have no speeds at all I would suspect either the blower speed switch and its electrical plug is at fault or the blower motor itself is bad.