Where is the AC orfice valve?

You will see a small diameter line at the a/c evap area that will have a threaded line. When you unthread and seperate you can look in the line that is exposed and see the orifice. There is a special tool needed for removal. Sometimes these can ger stuck and be removed with needle nose pliers. I have seen them stuck so bad that either you replace the evap or can try a patch kit after cutting the line.