To levy upon chattel paper, the levying officer shall take the chattel paper into custody if it is in the possession of the defendant or, if it is in possession of a third person, personally serve a copy of the writ and a notice of attachment on the third person.
If the levying officer obtains custody of the chattel paper or if pursuant to a security agreement the defendant has liberty to collect or compromise the chattel paper or to accept the return of goods or make repossessions, the levying officer shall, if instructed by the plaintiff, serve a copy of the writ and a notice of attachment on the account debtor either personally or by mail. (CCP 488.435, 700.100)