Have you asked for it? It might be as simple as that.
If there's nothing in writing on either side, I would think the dealer is obligated to return it, yes. Whether he'll make you jump and grovel for it, is another matter. If he doesn't play nice, notify your credit card company and they will probably reverse it. If they won't, then as a last resort, take the dealer to Small Claims Court and cut up that credit card and do business with a company that will support you.
This assumes of course that you did not sign anything to the contrary regarding a deposit refund.