the a/c system will remove moisture from the air. its that dry air that is blown across the windshield when you use the defrost. it will work with the recirc air. if you dont have ac then it wont work that well.
I know this is an old thread however, I will say neither one of my cowl vents are leaking BUT my 72 Grabber only has 19000 miles on it and is garage kept so... HOWEVER, I do have a site with an awesome pic right up of where the cowl vent is and how to plug with limited welding if anyone wants it. www.cameoclub.com/cowlventrepairs.html Scroll to the bottom for the Maverick/Comet specific walk through. You can also take the route they did at top of page but I dont really care for how that looks.
I did mine and love it, the A/C is more efficient. you have no hot outside air entering the car with the A/C on...I have no defrost problems and love the clean (painted) look. basicly the only paint that gets in the floor of the vents is overspray... on one July trip I took a pic. of my Wife wrapped in a blanket with the A/C on low...
Mine do not leak but I still try to avoid water getting into them. I have magnetic covers in the trunk for just those occasions.
My car had 19,345 miles on it when I got it back in 2012 and the cowl was ROTTEN! Mice had built nice little nests in and around the vent "hats", blocking the drains. My car also came from Ohio, in Mansfield. http://www.mmb.maverick.to/threads/paul-massons-71-grabber.92251/
Mine don't leak. I am really curious if any '73s had any rust protection in the cowl vents. I know that not all did. Or is it just a matter of what part of the world (climate) the car lives in.
Just found out yesterday that my cowl is leaking for sure. I have a '73, so I'm pretty sure at least mine doesn't have any protection. But my car is a florida car and has been since the original owners I believe.
Yeah, Im having a mouse issue as well. Little bastards keep finding a way in. They have a habit of nesting above my Tranny (the mechanical kind) and somehow getting nuts inside the hood support rails.
mine looks like it is galvanized no leaks at all but the windshield leaked when i got it can't get away with leaks on a old car they happen some where