Ac fan mode power consumption is lower because the compressor is shut off. The air condition is not generating chill air but you are getting ventilation which supports lower temperature by a few degrees.
You also need to know how the fan lowers the temp like an AC. Most cooling fans will have motors that build pressure on the intake air and force it out through the blades (or bladeless in some models) to add more airflow and a cooling effect to the air it moves.
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