The scope of this SAE Recommended Practice is to establish uniform test procedures for passenger cars, to determine whether the system is defined as a defroster or defogger, and to establish minimum performance requirements for each system. A defroster for purposes of this practice is a system which will remove moisture and/or frost from the interior surface of the backlight at -18 degrees C. A defogger is a system which will remove moisture and/or fog from the interior surface of the backlight at 4 degrees C. The test procedure is intended to simulate actual conditions by utilizing either a cold room with an appropriate device to introduce air flow over the backlight or a sufficiently large wind tunnel with ambient temperature control. The test procedure and the minimum performance requirements are based on currently available engineering data.