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Date: Wed, 15 Jul 2009 12:47:44 -0400
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From: "Robert Pastusek" <rpastusek@htii.com>
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Subject: [LML] Air Conditioning: Confessions of  LIVP Builder
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Jeff Ligner wrote:

For those who are building and considering the pluses and minus of 
air conditioning (A/C) installation in your LIVP, let me contribute 
my experience.  When I was building, I got to the point when adding 
one more system (ex, A/C) represented more work, longer delays until 
flying, more money, more weight, and more hassles.  I justified my 
decision not to install air conditioning based on ambient 
temperatures at altitude, efficiency of the third intercooler, where 
I expected to fly, abilty to divert warm turbo air prior to 
pressurization, etc.  In the end, these were not good reasaons to 
defer the A/C installation.

When I started flying I realized the temps entering the cabin where 
uncomfortably high if ambient temperature was >50*F, the solar 
heating inside the cabin is significant, the comfort of non-pilot 
passengers (who tolerate much less inconvenience) was compromised by 
added cabin stuffiness, and ground operations prior to reaching 
cooler outside air was really steamy at times (helped somewhat by 
opening the door a crack, despite the tornado of air).

I installed an A/C after the first year (details available 
separately), and must now acknowledge that it is a very important 
comfort item in the plane.  Passenger comfort, pilot comfort, ground 
operations comfort, cruise comfort, sunny days and overcasat day 
comfort, even winter comfort when clear skies and solar heating 
exceeds personal minimums.

So, for you builders who were like me, I encourage you to take a page 
from my retrospective lesson book and consider installing the A/C 
while it's easier, while the engine and airframe are not finished.

My contribution to the heritage of experimental builders.

Jeff Liegner
N334P


I would strongly second Jeff's views above. We didn't use the A/C in my
N437RP during this past winter, but when the outside temp started getting
above about 50 degrees, it became VERY useful. I made my own system out of
car components, and it works very well... with two exceptions. 

The condensation collection (old peanut butter jar) and automatic water dump
valve did not work during a recent trip to CA and back to VA, allowing water
to overflow into the pressurization bucket in the back seat and then into
the bottom of the airplane. No damage, but unsatisfactory. I made a new
auto-dump valve using a ping pong ball as the float and tested it this
weekend. Seems to work MUCH better than the little 3/16" ball I'd been
using...which kept getting stuck. The second issue is that I can't get
enough cooling air across the condenser during high ambient temp ground
operations. Result is that the system pressure goes above my 280 PSI
auto-shutdown limit within a couple of minutes of ground operations before
start/TO. It does better after landing, running for perhaps 5 minutes before
overheating on a 90 degree day. As Jeff notes above, at 90 degrees ambient
on a sunny day, the solar heat load inside the cabin is significant.

I've installed about the largest/heaviest condenser fans I am willing to
consider, run them continuously on the ground, and provided extra air flow
from the wheel well; still not enough air. I'm planning to live with this
one, as the A/C actually over-cools the cockpit in flight if left on max. I
would recommend installation of a thermostat on the evaporator output air to
allow some moderation of temperature...for the above over-cool situation,
and to keep the system from freezing up. I have an
automatically-compensating expansion valve that should take care of
freeze-ups, but I've found that under some humidity/pressure/temperature
conditions, the evaporator will ice up, blocking all cooling air... Backing
down on the thermostat just a bit to allow the system to cycle keeps the ice
away at lower altitudes. I've not had icing problems at the higher
altitudes...air probably too dry...

In summary, I do have some limitations on use of my A/C system, but my Judy
wouldn't trade it for an additional 20 KTS of airspeed! So there you have
it... 

BTW, I have a retractable belly vent that exhausts the condenser air when
the A/C is on, so no drag penalty when the system is shut down. That works
well also, but would be hard to install after the airplane is built.

Bob