I am changing the selnoid switch and replace fluids. Is it o.k. to use compressed air to flush fluid out of the converter before replacing new fluid? If not, please give suggestion.

I wouldn't use compressed air as you could damages it. The amount of fluid in the convertor that can't be removed by dumping it out is minimal. If you are doing this with the tranny in place I wouldn't even worry about the fluid. Simply replace the fluid that you drained and the filter and it should be good to go.