You may find that a compound noun doesn't have a space between the elements either. "Potato sack" is a phrase while bedroom is a compound noun made up of bed and room.
No, this isn't a compound noun. A compound noun is a single word (not hyphenated) which is made up of two (or more) words which can stand alone as individual nouns. eg bedroom is made up of two nouns which can stand alone : bed and room. The English language loves to invent new compounds whenever the need arises.