Try this, you will need a hammer and a long steel rod 1/2 " diameter, place end of rod on the left edge of the big nut and hit rod with hammer, hard!
This will loosen the fan nut, it turns to your left when standing in front looking at the engine, best done with belt installed as this will hold pump pulley in place. Works every time if done correctly! When ready to tighten it back, the same just tap it to the right this time.
At the shop i use an air hammer with a 15" punch attachment but you can do it the old school way just as well. Or buy, rent the tool to do it with!!