Whenever I try to use the Refine Edge tool for a mask, it will not add what I have selected to the mask, rather it will take it away. This always happens when I use the tool, no matter what view I am in. Any suggestions?
I take it you are starting with a layer with a layer mask, and using Mask Edge in the Mask panel? Have you got a copy of the same layer underneath it?
The shift edge slider is fairly subtle. Try draging it to 100% one way then the other. Do this with a layer filled with a contrasting colour immediately below it in the layer stack. You'll see a difference, but it is not much. If you use big values with the feather slider, now that WILL be obvious!