2002 Nissan Maxima Question: What causes the fan for my heater/air conditioner/defroster to stop working?

Various settings did work, but the fan would shut off and remain off unless the automatic locks were used. Then it would run another 10 seconds or so and turn off. The dealer played with the locks and looked at some things and declared it fixed. The fan worked all the home, but no longer works at all. Is this a bad motor or bad electrical connection? What will something like this generally cost?