For those of you in here wondering about increasing the airflow (by adding an additional outlet vent) compromising the efficiency of the unit, and also those that are basically saying "BTU is BTU and you're not going to effect the rated output of the AC unit", try my mod in this thread. Here's why...
Reducing evaporator airflow will decrease evap temps. (I think I posted something about this in another thread about adding a second AC?) Increasing the amount of evap airflow will do the opposite, it will raise evap temps. It's that balance between the perfect airflow creating the perfect evap temps that the manufacturers like Coleman shoot for. Well guess what? Coleman has no idea what a coach builder like Thor is doing to that airflow when they put their AC unit on a coach. The 15k Mach 3 puts out X amount of cfm. (didn't go look it up.) What happens to that cfm number when it's put in a coach with no ducting, 4 ducts, 12 ducts or 80 feet of restricted roof ducting? It's no longer anywhere near optimum.
What you guys adding the outlets are doing is raising the evap temps because it's simply trying to cool down more warm air. What you guys that are closing outlets in areas of the coach that aren't being used are doing is the opposite, you're lowering the evap temps. You're basically changing the cfm of the unit.
I'm not saying any of this is good or bad, just identifying the physics of it all. So here's why I posted the link to the thread with these evap thermistor mod ideas... Changing BOTH airflow and evap temps can drastically change (improve) AC efficiency. So for you guys that are adding outlet vents or basically increasing evap airflow, try moving or removing the thermistor too. Increasing airflow will reduce the chances of evaporator icing.