Hyundai CC Valve

My girlfriend took her 02 Hyundai Sonata in for a check up. They gave her a list of things that needed to be done. I can do the majority of things listed, but they said she should replace the CC Valve & Filter.

I don't know what that is & am finding nothing helpful when doing an internet search. What are they, where are they, how tough is the job, etc?

Thanks
-E