Halakhah к Шаббат 4:4

The Sages instituted that the ḥazan recites Magen Avot or the Berakha Me’ein Sheva (a summary of the seven berakhot of the Friday night Amida) after Ma’ariv, to serve as a sort of Ḥazarat Ha-shatz (see Peninei Halakha: Shabbat 4:2 for further study).

He notes that in most refrigerators, metal is not heated until it glows. He explains that even though there are gases that are heated in the refrigeration cycle, heating these gases does not constitute an act of bishul (cooking). Among his reasons are that the gases are not heated by a fire source (see Rambam's Commentary to the Mishnah, Shabbat 4:1) and that heating a gaseous substance does not constitute bishul.