Is one allowed to adjust the shabbos timer on shabbos so that the air conditioner should shut off later than originally set before shabbos?
Several authorities permit doing so, the deferral involving no melachah. Some are stringent in this matter, comparing it to adding extra oil to a candle thereby causing it to burn for longer. However, there is a significant difference in that extending the timer only delays the switching off, whereas oil actively burns.
One can rely on the lenient opinion.
See Shemiras Shabbos 23:22, 13:25-27; 12:14; Yabia Omer 3:18; Az Nidberu 14:11; Minchas Yitzchak 9:38).