Seems to be a more common problem then you would of thought. After reading through several forums the consensus for this is that there are several things that can happen. Most of the occurrences happened with the heater/blower circuit. Some think it's caused by cheap chinese fuses. The fuse may not have been seated correctly. The blades may have had some corrosion present. The holder may have had some corrosion present. I'd take some fine sandpaper and clean up the female socket as best you can. Clean/sand the blades on the fuse and apply some dielectric grease to the blades to form a better contact.