69 Barracuda. When it rains I get water coming in the two fresh air vents.
How do those drain, and where to look for blockage?

Ill be watching this as well since i have the same problem.

are the drains full of leaves and dirt? look under the hood near the windshield sorta.

I guess what I don't get is where exactly the water is supposed to part company with the air?

It seems the air for the vent comes from the cowl area - via the louvers on the cowl. But where are the water drains, and how to get at them?

The drains are in the area where the hinges drop into inner fender area, you can see it with hood open where the cowel pieces come together. I'm sure there's junk plugged up in there and you may be able to drag some out of there with bent coat hangar etc. You will not have the first mopar with this problem.

I'd start by dropping the vent can on the drivers side and heater box on the pass side. The plenum is basically a lip about 1 inch or 2 into the cowl area. If you are lucky, the accumulated leaves and crud haven't rotted a hole in your cowl. Clean away the leaves and such by getting your hand up there and pulling out what you can. A small vacuum hose can be used too.
Next thing to do is clean the drains at the edges of the cowl. You need to remove the splash shields between the inner fenderwell and fender. Right at the pinchweld seam is a drain. Use a coat hanger to clean up as much as possible. A hose and running water helps flush out the rest. BTW, that same crud in your cowl is what settles to the bottom of your fender corners and rots them out.

Now is also a good time to replace your wiper pivot seals, if you haven't already. That's the other place water gets in.

Thanks for the replies.

Sounds like what happens when the gutters on your house get filled w/ leaves - it causes the water level to go higher which makes the water spill over the sides of the gutter.

you could also try an air gun with a long plastic hose attached to air gun to feed where the slot is (under hood hinge area) and blow the hole out, then blow from the cowl down back and forth for about an hour and you should get most of it out. when I did my car it seemed like the leaves and junk just kept coming out seemed like forever.