Personally, I don't think it should be a full refund. For an item of this value, the buyer should also bear the cost as well. If I were the buyer, of course I am quite angry because the fan is faulty, but asking for refund is probably my second option.

Why not try install a new fan or fix the fan syapl? You said yourself you are quite familliar with electric board and stuff.

This is my 2 cent only.