A collection of account receivable will affect what account?

A collection for an account receivable will affect two accounts. Cash and the Account Receivable that it is related to.

For example, a customer has purchased a computer on account for $1500 and they pay you $500 towards the balance, the two accounts will be

Cash (db) $500
Account Rec-*customer name - (cr) $500

Not only did you receive cash, which increases your cash (debit) but the customer paid toward his account and it reduces the amount he owes (credit).