Slipstream - August 2011

Cliff’s Ramblings
By Cliff Blackshear
It has been in the 100F/37C range
for weeks now. I want to make some
suggestions to all.
I’m gonna go old school here. I honestly
have not looked into a recent owner’s
manual for any Porsche model to see what
the factory currently suggests to maximize
cooling efficiency in hot weather.
But, I know what works and why it works. I will not go into
the refrigeration system doings and heat removal from air
etc. Nor bore you with the latest climate control monitoring
sensors and how a micro processor responds based on driver
inputs, temperature sensor data etc. The systems today, in
any vehicle, including any new Porsche, are very complex.
Even the sun intensity and
angle of light is now a part of
how the systems work in all
our cars. Plus, air quality is
measured with a smog sensor.
Over the years, I have found
myself in repair situations
that dictated my going to a
Porsche and measuring the
inside cabin temperature after
the car sat out in 100+ degree
heat, with the windows
shut, for hours. The highest
temperature I have measured
was 165F on black leather
seats in a 911. I regularly
see 130F + temperatures on
a daily basis. Light colored
materials absorb and maintain
solar radiation much less than darker materials. You folks
all know that. When you take an infrared monitor out and
measure interior temperatures, the reality really strikes
home, especially if you measure the temperature of the
metal top of a black car and then a white car.
If you have to park in direct sunlight for hours before
returning, put a sunshade inside the windshield. Get one that
reflects ultraviolet light. When you get in, start the engine,
roll down all the windows. Turn the AC on and set the fan to
it’s lowest setting. Wait about one minute and preferably be
moving as soon as possible.
Having the engine off idle and air moving over the front
condenser is extremely helpful to the refrigeration system.
1500 RPM or more will allow the refrigeration system to
get on point efficiently. The car moving will maximize air
movement over the condenser and get refrigerant moving
Jeeezzee It’s Hot Outside Lately
heat from the cabin much quicker. The lowest fan speed
will allow the AC evaporator to reach its maximum efficient
cooling ability quicker. Have the system set on outside air
and let it start out cooling air drawn in from the outside.
After about one minute of suffering in the heat (which in
my experience yer gonna do for a longer period if you do not
follow my suggestion), switch the system to recirculated air.
Next, ramp up the fan speed after rolling up the windows.
The air coming through those vents needs to be recirculated
air and not outside air. Continuously recirculating that cooler
air maximizes efficiency and is worth about five to eight
degrees of cooler outlet vent temperatures. I have measured
it in many test situations over the years. 944’s especially
suffer if their recirculation system is not working correctly.
On average, it
takes four to seven
minutes to feel some
relief from the heat
in any vehicle in
100F temperatures
when the cabin
temp is 120F+. I
have measured the
cabin temperatures,
monitored the outlet
temperatures and
refrigerant pressures,
while noting the
time, speed, driver
settings etc. Recently,
I have made multiple
excel sheets noting
this information and
forwarded it to Porsche engineering to help them further
their quest to make their climate control systems more
efficient. The systems in today’s P-cars are as good as any
other manufacturer in my opinion.
Car color and interior color is a huge factor.
I’m Just Sayin’!
And I’m thankful to be working in an air-conditioned
shop. I worked in multiple, no AC P-car dealers for 29
years. What a beating…….. Sounds crazy, but I would not
trade the experience for anything.
Cliff
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