The blower motor resistor may need replaced. It is located up under the dash on the passengers side. It may be extremely hard to see as you may not be able to get your head up under the dash far enough to see it. There will be a bundle of wires, about 4 or 5 wires that hook into a connector that is plugged into the the blower motor resistor. Two 1/4" screws hold the resistor in place. When you get it out, you will be able to see that it is burnt. It may be the coilspring type, or possibly the circuitboard type. Either way, you should be able to tell if it has burnt through. The replacements are about $25-$35 at your local parts store.