Output Spanish from us7ascii clob table?

I have a clob table where some of our users are entering Spanish characters that aren't pulling right from our sql -- like ascii 150 ú. It will show a ┐ in SQL Plus and ﾖ in our ORDS output. If I use the function ascii, it tells me it is 150.

I tried convert(my_string,'us7ascii','utf8') and it shows a question mark.

The db NLS_NCHAR_CHARACTERSET is UTF8 and the NLS_CHARACTERSET is US7ASCII. I tried converting the column from a CHAR to NCHAR and the existing data doesn't do anything different.

Is there anything I can do to that column or is there some sort of conversion ability that I can use so my REST Data Services and other applications display non-English characters?