What does it mean if there is a urine smell coming through the front vents of a car?

Usally the AC Drain is stoped up & there is standing water & debre in the evaperator case U need 2 take something soft & stick up through the ac drain under the hood of the vehicle,nothing sharp or U could puncture the Evaperator core.compressed air usally works good.

Answer

Sounds like you have a leaking heater core. The smell that you describe is the smell of eng. coolant. If you turn your heater on to full max it will get stronger. Or, a cat slept on your car and you know what that means. Cat piss. It happen to me years ago.