John, I have an automotive type of Air Conditioning in my L4P but it is not that easy to solve all the issues. Mine is an AERO COOL system (http://www.flybymike.com) sold through Lancair. You can't use the "mixing valve" for AC because that is where your Pressurization comes in and you need an emergency pressure dump in case of smoke in the cockpit or several other abnormalities. Also, the air from pressurization coming in the is warm and with that routed by your feet and the AC above you remain just right.
BTW, the AC is a No GO item for me now, it is so so nice. It was 100* in Bend last week and 104* in the cockpit when I closed the door and the AC had it down to 84* after only about 2 or 3 min. The air at the back of my head was 70*. I turned it off climbing through 14K after having it on low in full sun. When I landed, that airport was 80*, and with it on Lowest Fan and Temp. setting, I was too cold in my shorts and had to turn it off while taxing. It has paid for itself many times.
Demo's at OSH if I'm parked where I can start it.

Jim Hergert
N6XE, "An Sex Y" L4P