I have replaced both the blower switch and the blower resistor on my '96 Jimmy, and everything works fine for a short period of time, then the fuse to the blower motor fails.
Just today, I replaced the fuse and, with the vehicle at rest, ran the AC and the heater at all switch positions and at all speeds for twenty minutes. During this time, I hit every switch in the car to see if by switching something else on I could cause the blower fuse to fail. Everything continued to work flawlessly.
Shortly thereafter I had to make a short trip, so I tried running the blower and it worked fine for about two minutes, but then quit. Once again the fuse had blown.
If anyone has any idea what might be the problem I would appreciate a heads up.