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With Automatic Climate Control and the air conditioning set to on I was wondering if the compressor is running all of the time regardless of the temperature selected. My point is if you set the temperature at for example 78 degrees vs 65 degrees are you theoretically getting better fuel economy/performance.
 

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DWF - automatic climate control usually also acts to control humidity so even if your set point temperature is above the ambient temperature, the compressor may still run to bring the humidity of the passenger compartment air down when the a/c button is on. The cold, dehumidified air is then blended with warm air before being fed through the vent at the desired temperature. The extent to which the compressor runs will obviously depend on the ambient humidity versus the comfort-level humidity in the software that controls the ACC unit.

From the manual, the compressor does not operate at ambient temperatures below about 5C.
 

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With Automatic Climate Control and the air conditioning set to on I was wondering if the compressor is running all of the time regardless of the temperature selected. My point is if you set the temperature at for example 78 degrees vs 65 degrees are you theoretically getting better fuel economy/performance.

As I understand it, the AC system only makes one temperature. When you turn it up from 65 to 78, the system just blends in more warm air from the heating system.
 

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However, the a/c compressor will disengage if you get the RPMs up high enough (somewhere over 4K or so). This does two things: it keeps the compressor from over-revving and it frees up the horsepower needed to drive the compressor.
 

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However, the a/c compressor will disengage if you get the RPMs up high enough (somewhere over 4K or so). This does two things: it keeps the compressor from over-revving and it frees up the horsepower needed to drive the compressor.
That makes sense. I guess turning teh A/C off would be prudent when DE-ing the car. But the windows are down anyway. So let me get my check list right:

Before I go on the track:
A/C off
Wing Up
PASM to Sport
Sport On
Seat Belt and shoulder belt cinched tight.

Ed
 

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With Automatic Climate Control and the air conditioning set to on I was wondering if the compressor is running all of the time regardless of the temperature selected. My point is if you set the temperature at for example 78 degrees vs 65 degrees are you theoretically getting better fuel economy/performance.
DWF,

I notice a definite decrease in MPG and prolonged acceleration with my Mini when the AC is on. As a matter of fact, I have to launch it at about 500 rpms higher to avoid stalling in 1st gear. The AC probably takes 5-8 HP off the 115.

The Cayman is much more powerful, so I doubt that you would feel the difference either in fuel economy or performance. As a rule of thumb: European car magazines state that you will consume 0.5-1 liter more / 100 kms if your AC is on (1 gallon is 3.78 liters and 100 kms equall 62 miles).

Tamas
 
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