CA Civ Proc Code Section 700.170

(a)

Unless another method of levy is provided by this article, to levy upon an account receivable or general intangible, the levying officer shall personally serve a copy of the writ of execution and a notice of levy on the account debtor.

(b)

If a levy is made under subdivision (a) and payments on the account receivable or general intangible are made to a person other than the judgment debtor (whether pursuant to a security agreement, assignment for collection, or otherwise), the levying officer shall, if so instructed by the judgment creditor, personally serve a copy of the writ of execution and a notice of levy on such third person. Service of the copy of the writ and notice of levy on such third person is a levy on any amounts owed to the judgment debtor by such third person.