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As I understand, the basic function of an indoor air conditioning system is to pass air through cooled surface (tubes) which makes air cooler and hence it reduces room temperature.

So my question is, will running AC on low fan speed cool room faster? Since air is slowly circulated around cooling surface and gets more time to exchange heat.

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Energy transfer (aka pulling heat out of air) depends on the temperature difference.

So you quickly fall into diminishing returns when you try to cool the air down those final 2° when in the same time you can cool the same (warmer) volume of air by 15°.

  • My room temperature is 30+ degrees. So there is a bug difference in temperature already. – Waleed May 28 at 6:44
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No, the maximum fan speed is the best for AC over the long run. The biggest difference in temperature between the incoming air and the evaporator coil makes the most heat transfer. Also, the extra airflow doesn't make you feel uncomfortable. This is how central air conditioning is set up in homes.

In short term if you're going to be sitting in a car and want it cold now, then a slower fan setting will blow colder air, which feels nicer than a lot of slightly cool air.

You might be getting confused with heating fans. Too much airflow will make a lot of 80F heat, which will feel colder than slightly less 100F heat. That's why home furnaces typically run the circulation fan slower for heat and faster for AC.

  • We don't have a central air conditioning system, in my office we have a room with 1 Split AC. Just like a car ? – Waleed May 28 at 6:29
  • @Waleed A mini split AC unit cooling a single room would probably be best operated like a car's AC. If you're right in front of it, slow speed will feel colder immediately, but fast speed will make the entire room colder slightly faster. Running those fans on high can be noisy too, so do whatever is the most comfortable. – Dotes May 28 at 12:57
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I will say it depends, I can agree with both ratchet freak an dotes in part but each system is set up differently, a central system that is not properly insulated a higher air speed may be better , I know on my mini split it auto the fan speed varies based on the load, grand kids start coming in and out it kicks up to a higher fan speed and the compressor loads up or is running at full speed, when the area gets back to target both the fan and compressor slow down, so depending on how your system was set up even a mini split can be different but usually a high speed for AC is the best, more air exchanges less chance of the evaporator icing up.

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