blower does not work on 2008 Ford F-250 Super Duty

blower does not work but if i hit a bump in the road it starts to work

check the connector at the blower motor and the blower resistor. they are under the right side of the dash behind the glove box.

1 more answer
Yes you should always check the condition of the connectors, Ford's have had pig tail issues for some time know, but that said, if all looks good and you can recreate the symptom by lightly taping on the blower motor with the but end of a screw driver, and all the blower speeds are working, you will need to replace the blower motor. Some of the replacement motors come with a new pig tail you should install damaged or not. The labor time to replace this motor is not even an hour, the best way to replace the pig tail is solder and shrink wrap.