Is one allowed to adjust the shabbos timer on shabbos so that the air conditioner should shut off later than originally set before shabbos?
Answer:
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).
Best wishes.