On a hot day and traveling in a car, which method of keeping the occupants comfortable with the A/C is more energy and fuel efficient?
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Set the thermostat to a lower temperature and keep fan speed to the lowest setting
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Set the thermostat to a slightly higher temperature and compensate by setting the fan to a higher speed so you can feel cool enough with the breeze
There is some optimal amount of thermostat vs fan speed. Whether you’re better with a lower thermostat and higher fan speed or vice versa depends on which side of this optimum you’re on. We as random internet strangers have no way to find this.