This International Standard specifies the test method for passenger car (term 3.1.1 in ISO 3833:1977) windscreen defrosting systems when these are fitted. It is not necessary for the tests to be repeated on types of power-driven vehicles which do not differ from one another in respect of the following essential features which affect defrosting performance: a) shape, size and surface characteristics of the windscreen; b) characteristics of each system designated by the vehicle manufacturer as contributing to windscreen defrosting. This International Standard does not specify reference areas or levels of performance. NOTE 1 It may be possible to carry out tests of a similar nature on front windscreens and rear windows simultaneously. The test condition of − 18°C ± 3 °C specified in this International Standard will meet the majority of cold climatic requirements. However there may be instances where lower temperatures are encountered, and such conditions may be dealt with in a future document.