The scope of this SAE Recommended Practice is to establish uniform test procedures and minimum performance requirements for passenger car windshield defrosting systems. It is limited to tests that can be conducted on uniform test equipment in commercially available laboratory facilities. The test procedures and minimum performance requirements outlined herein reflect the extensive knowledge and experience which automotive engineers have accumulated in development of windshield defrosting practices. Current engineering practice prescribes that for laboratory evaluation of defroster systems an ice coating, rather than frost, be applied to the windshield to provide more uniform and repeatable test results, frost formation of uniform density being the more difficult to accomplish. The time element for ice removal, therefore, is longer than that required to remove frost, which is the prime purpose of the defroster system. In accordance with established policies of the SAE Technical Board, all portions of this recommended practice will be reviewed and revised to reflect technological progress regarding vehicle defroster performance. NOTE: Because of such differing factors as greater vehicle size, engine operating characteristics, windshield configuration, etc., a separate SAE Recommended Practice is under development covering test procedures and requirements for defrosting systems of trucks and multipurpose vehicles.