Yes, the heater core/evaporator box has a drain. Generally it's under the heater hoses or the A/C lines going into the firewall. If the smell is a dead animal, you will have to remove the box and clean it. I have found mice in the blower motor squirrel cage. If it's a musty smell, clean drain and there is a spray that you can introduce into the A/C that will get rid of the smell. Can't remember the name. A/C deodorizer? I have blown the drain with air and used a coat hanger to clean the drain. Don't go to far with coat hanger as you might poke a evaporator or heater core.:vs_cool: