climate control fan problem on 2002 Volvo S40

The climate control fan had been acting erratic.. speeding up and slowing down at will. Now it is simply on high all the time. I can't change it. What could this be and how much might it cost to have it fixed? Can I fix it myself?

Asked by for the 2002 Volvo S40
These cars have a resistor that controls the fan speed, it may be that the resistor is failing.