So... you are driving along and the fan just stops working, or you get in and it won't go on, but sometimes it does, am I right? I'm pretty confident in this guess, it has happened to me before, and good news: It's a fast cheap fix.
This is almost certainly the relay under the hood. Look in the box on the right fender for the Blower Motor Relay. These are cheap standardized relays any parts store will have on the shelf. Now, I almost always like to see more troubleshooting on a problem but for this... it's so common, I replaced this relay twice over the years and it's a good spare to have in your glovebox anyway because the same relay is used for other functions such as the fuel pump.
So, I'd just go ahead and replace the relay without digging too much further. And like I said, if you are using this as a daily driver or some other important thing, buy a spare.
