2005 Park Avenue Ultra where t the drain plug for car

There is none....

The condensate drain is open ended......the drain tube exits through the firewall, and there is usually a rubber elbow, pointed downward, to allow the condensate to drain......it'* possible there could be crud in the end of the elbow, blocking it.....it is located in the engine compartment, passenger side, looking at the serp belt, it should be 2-3 inches, to the right of the belt, about 1/3 up on the firewall....elbow can be pulled off and checked....