I describe that fuse on my blower repair page:
- http://www.4crawler.com/4x4/CheapTricks/Blower.shtml#BlowerResistor

If you find the fuse blowing again, you might have a look at the brushes inside the blower motor. When they start to wear out, they can cause excessive current flow in the motor. When mine went, I never blew that fuse, but I did have trouble with the blower motor overheating and shutting down periodically:

- http://www.4crawler.com/4x4/CheapTricks/Blower.shtml#MotorRepair