With some care, washable filters can be reused numerous times. After removing this kind of filter from the device soak it in warm water using an mild detergent. Then, rinse thoroughly. Make use of a soft brush to get rid of dust and dirt and allow it to air dry. Once the filter is dry, put it back in place. The majority of portable air conditioners come with a prefilter, which helps to prevent dust and larger particles from getting into the unit. The main function of the pre-filter is to increase the life expectancy of the air filters inside the unit. The filter should be cleaned at minimum once a week.