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
It depends on a large number of factors. Largely it doesn’t matter.
What I personally do is start my car with a low fan speed, let the evaporator cool down, then start cranking up the fan speed so I feel the cooler air. When it’s really hot out my AC can’t keep up in my car, and blasting the AC essentially guarantees that I’ll never feel cold air. I’ll just have a cooler ambient temperature, but the air blowing at me (that I’m feeling) is warmer so I feel hotter.