It should come as no surprise that fridge dryers cool air to remove moisture. This process occurs with an air-to-heat exchanger and air-to-refrigerant exchanger.
As the temperature drops, air moisture condenses and is drained. After this step, compressed air is reheated to room temperature, lowering the PDP and preventing condensation on the pipes.
Read this article to find out all advantages of a refrigerant dryer.