The short answer is yes; it is more energy-efficient to leave your air conditioner on all day. The long answer is a little more complicated. The most effective way to run your air conditioner is to program it to keep your space at a specific temperature throughout the day, whether it’s the suggested 78 degrees or slightly cooler. Surprisingly, the worst thing you can do is turn the air conditioner off completely. Yes, you save power when it’s off, but it’ll inevitably have to work extra hard to regulate your space’s temperature and humidity when you need it again.