car fuse didn't blow?

Never saw this before, but I've not seen a lot of things. The correct amp size for that socket is a 30 amp fuse which is what was in it. Blower motor stopped working and I pulled the one beside it to check it. It was good but then when I tried to pull the one beside it, it wouldn't come out. Upon further inspection, the plastic around the fuse had somewhat melted and discolored as had the fuse. But, the fuse link still appeared to be intact.

The fuse that melted, I believe was to the rear window defroster and not the blower motor.

Ever heard of such a thing? That is, a fuse that didn't blow, discolored from likely heat and the plastic around it melted?