I had the same thing happen! Mine had power to the fuse and through the fuse, but the other end of the fuse wasn't making a good contact in the clip. Mine wasn't corroded, it just needed some cleaning! As a note to others: when checking fuses, probe the clips and not just the fuse!
find the hot wire to the switch. the wiring to them things is crazy I finally hooking it up to an different fuse box he's got medium and high heat. but it does not work on low and it could be the heater switch it self