The white keys on a PA, piano, keyboard, whatever, correspond to the notes on an C accordion.
So you can figure out what you can do on a CA and what you can't. Not necessarily in C but of course also in G, and Dm, Am and F are also possible to some degree.
Of course you can figure this out on a C box rightaway, but a keyboard offers a fresh point of view. Litterally, because now you can see all the notes on the keyboard. No black keys. No pushing and pulling. Easy!
Any song or tune playable on those white keys is possible on a CA. Of course, for other keys you need a different box, but the idea stays the same.
I hope this makes any sense!