What is the difference between the ac expansion value and the evaporator core? on 2001 Nissan Frontier

Had my ac compressor replaced; they did not replace the drier. Now my air speed control only blows on on speed and under the hood is iced up (a long tube running into the back of the dash. I'm told I now must replace the expansion valve and evaporated core due to debris?

Asked by for the 2001 Nissan Frontier