After a long period of use, the accumulation of dirt and moisture will reduce the performance of the car air conditioning unit. This is also a favorable condition for mold and harmful bacteria to arise. In addition to creating an unpleasant odor on the car, if exposed regularly, your health will be affected and susceptible to respiratory diseases. To protect the health and air in the car on every journey, every 20,000 km, the driver should clean the indoor unit once. -Just need to clean about 20 minutes, save money and save time 3M AC Evaporator Cleaner 1L Car Indoor Cleaning Solution