I have a 2004 style side crew cab and blower motor works only after going over road bumps. Replaced relay but only fixed problem for a while. When it comes on all speeds work fine and I can turn it on and off. It happens two or three times a day. Any ideas would be helpful.

 

Sounds like a loose connection.

 

1. This is the 1997-2003 section.

2. There is an electrical-specific section - ask a Mod to move yer Q there?

3. You'll need to do some basic troubleshooting - if that's beyond you, take it to a shop. Pop the hvac control panel and check the connections. Remove & Inspect the resistor pack, and it's associated connector. Yer looking for burns/corrosion, looseness, etc.

https://www.f150online.com/forums/ar...emtc-hvac.html

https://www.f150online.com/forums/ar...igh-speed.html

4. Avoid any bumps

good luck