Another aspect is the large amount of outside air that is sucked in under every a/c setting.
Put it on the snowflake (the least amount of outside air) and feel the rush of outside air going into the hood vent.
Consider that the outside air being sucked in is well over 100degf in stop and go Texas freeway traffic and there's little chance for the a/c to keep up.
I tried making a restrictor plate for this intake, but it's clear that the interior vent is not enough to pick up the slack...
There's probably a way to improve the air flow from the interior into the a/c, but I haven't explored.
I not only would like to improve the a/c efficiency, but considering I live in a city that is always battling for #1 in polution, I don't want that much outside air coming in...