If it only works on high, replace the resistor. Its a pretty easy job. And the part should only run you about $15. If it doesn't work at all, then you should start looking at the blower motor or associated wiring.
2010 Wrangler Unlimited Rubicon- Teraflex 6" Elite LCG Long Arm, Fox Adjustable Remote Reservoir 2.0 Shocks, Tom Woods Front and Rear Driveshafts, Cooper STT Pro 37/12.50/17 tires...