No, that is not a Swedish sentence. 'Kall' is the adjective (cold), 'Fryser' is a verb (like 'freezing'). So if you want to ask if a person is cold, you would say. "Är ni inte kall?" or "Är du inte kall? which is possible, but not exactly the same thing as 'fryser', where we think of a person more or less shaking because of cold.