Every car air purifier comes with a life span, and it can work for some duration of time. It all depends on the brand you have chosen and the facility it provides. Few car air purifiers come with the provision of replacement of filters while few brands do not have the option.  When you feel that the car air purifier is not working properly, then it is time to replace the filters. If your brand does not allow the possibility of replacing the filters then replace the air purifier.