I fly a non-pressurized non-turbo Lancair IV.  It has no air conditioning and I do not need it living in a fairly cool area.  In the desert, it is usually just fine at 10,000 feet.  I found this to be also true with my Turbo-Retractable C-182RG which was based on Northern California, and flew a lot in the desert regions, including summer.  Holding the door open a bit on the ground has not proven to be a problem.  The cabin stays 70F with 60F OAT while in the sunlight.  However, I do have additional ventilation in the form of two small NACA scoops and eyeball vents down in the pilot and co pilot foot wells.   These work great and I consider them mandatory for a non-P aircraft.  I think they are standard on the two place aircraft.

 

For east of the Mississippi with 90 by 90 as the normal temperature and humidity, I would consider air conditioning mandatory for at least humidity control all summer long.  Fortunately I could usually avoid flying in hot and humid conditions and so never missed the AC in any of my airplanes.

 

However, I think the P models can benefit from a bit of additional work to cool pressurization air, particularly when operating in the middle altitudes (teens) where the ambient is still comparatively warm in the summertime, and the heat of compression becomes appreciable.  I have noted that the pressurization air passes forward to the third intercooler for reduction in temperature, then traverses the engine compartment back to the firewall via 1 inch (I think) SCEET hose.

 

I believe that the cool air exiting the third intercooler is reheated a little bit passing through the hot portion of the engine compartment back to the firewall.   This length is nearly four feet long, and that has to have some heating effect on the pressurization air.  The ambient air temperature in this portion of the engine compartment is typically 100-150F above ambient.  The heating effect may not be much, but even if it is as little as 10F, the difference between 60F air entering the cabin and 70F air can be appreciable in terms of cabin comfort.  So I would want to minimize the re-heating of pressurization air as much as possible.

 

How to minimize re-heat with the SCEET hose?  Here is one idea.  Assuming that the pressurization line is 1 inch diameter, consider slipping it inside 1.25 inch diameter hose to act as a jacket and create a bit of an air gap.  Better yet, take the one inch line, wrap it with felt insulation about 1/8” thick (Aircraft Spruce has some 1/8 inch thick firewall blanket material that would work), secure with safety wire, and then pull over a jacket of 1.5 inch diameter hose outside to act as a protective jacket and further improve the insulating effects.  I would expect this will go far to minimize the re-heat of the air from the third intercooler and make the cabin a lot more comfortable in the summer.

 

Fred Moreno in the surprisingly cool SW corner of Australia