You could do the old "put a paper clip in there where the fuse goes, then fix whatever catches fire" diagnosis, but I don't recommend it.
Am I to understand that it doesn't blow the fuse until the blower is turned on?
Just so we have our terms straight, you said the fan was replaced. The blower for the system, or the radiator aux cooling fan? And this was the A/C relay you replaced?
OK. Get back to me on that so I can understand what you've done.
What you need to do is try to isolate what part of the system is over loading. If it is fine until the blower is turned up, I'd think that's where the trouble is. If it blows the instant the compressor engages, then there is the problem. If you keep it away from the A/C selections, and just run the blower on heat, does it work or blow the fuse?
Look at the pigtail where the wiring connects to the compressor. Make sure it isn't melted, chewed up or anything, and follow that wiring as far as you can to make sure it isn't laying on something hot.
That's a pretty hefty fuse, whatever is blowing it is probably shorted straight to ground somewhere.
See if that blower works OK in a non-A/C position and get back to me.