My resistor pack failed a couple of years ago, and I bought a new one. It failed within two days. I sent it back a defective, but the second one blew quickly as well. I figured (thanks to teh Brickboard) it was because the fan motor was stiff and worn,and turning so slowly on low, the heat built up and blew the thermal fuse in the resistor pack.

I hated buying yet another resistor pack, along with a new fan motor, (and teh embarrassment that it was my problem, not a defective pack)so I repaired the thing by replacing the thermal fuse. It looks like a capacitor, but is simly a fusible link based on temps. It was only a couple of bucks at Radio Shack. Use a pair of hemostats or maybe a pair of vise grips to act as a heat sink between where you are soldering and the fusible section in the middle, so you don't ruin it while soldering.

It is still working well today.

Now if I can only get the car to start right......but that'a another thread.
Ron