Fan only works occasionally-usually after I hit a bump

Sounds like some loose wiring. First check the fuse is firmly seated in the fuse box. Then access the blower motor assembly in the dash, typically it's through the glove box door. Make sure the harness connector is also well seated. If there is a ground wire make sure that is also well connected. Play with the fan selector switch, if it feels loose or intermittent that may be bad. If you don't see anything obviously bad you may need to use a multimeter and follow a wiring schematic to trace the wiring harness.