I believe that they cool air in the same way, using Freon in a cycle to take the heat from one area and moving it to any other by way of a heat pump.
Air conditioners also control humidity and other factors in order to 'condition' the air to be comfortable for humans. Fridges don't do this.
A fridge would provide a similar cooling effect to an air conditioner if you stuck the back of it out a window. However I doubt it would be as strong as it isn't designed to cool large volumes of air
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