I just fought with this very problem for over a month, as time would allow me to do so. If the plug that PT speaks of doesn't fix it after cutting and splicing, odds are pretty good it goes back to your fusebox under the drivers side dash, which are prone to going bad. You'll want to check voltage at the #6 and #7 fuse and if they register 12v-ish, then it very well may be your fuse block.
A good work around I found in several forums is to access the back of the drivers side fuse box where you'll see several plugs. You want to take the Brown/pink wire from the bottom plug, and the Brown/red from the far left side plug and splice in a fusable link. Button everything up, plug in a 30amp fuse and that should do it. The fan should sing after that. You're ultimately bypassing the fuse block with this method. May not be the best, but definitely more economical than buying a new fuse block.
And just know....your hands are going to get pretty beat up and cut up when working in that tight space with that fuse block. But, it's worth it to have heat again!
Hope this helps. Good luck!