Quote:
Originally Posted by JohnS
Hey guys,
Once you turn the A/C on, does it matter whether you run it at a low level as opposed to MAX? In other words: As far as gas consumption goes, does setting the controls to a higher temperature and lower fan speed use less gas than full-on cold and blast the fan? Or is it that once you turn the A/C on, it uses the same amount of fuel no matter what the setting?
Thanks in advance,
John
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Hi John,
It depends somewhat on the car. There are 3 control systems used.
On smaller cars the A/C compressor cycles, only running when the cabin is warmer than the thermostat setting. Using the lowest fan and warmest setting that is comfortable saves fuel.
Some larger cars; when you call for A/C the compressor is engaged and cabin temperature is regulated by also running the heater.
On hybrids with high voltage systems the compressor is run by a variable speed electric motor. It runs just fast enough to give the desired cooling.
In all cases the A/C system uses less power and therefore less fuel if you stay on the edge of comfort. Running the A/C full blast uses more fuel.
An air condioner is a heat pump. It uses power, usually from the engine, to move heat out of the cabin air. The amount of power required from the engine is the amout of heat removed divided by the "coefficient of performance." The COP depends on system design and outside temperature.
Car A/Cs have COPs from 3 to 5 and usually about 50,000 BTUH capacity.
-mort