Summer and saving money with the AC?

So my Japanese roommate mentioned to me that turning the AC on and off actually costs more money than just leaving it on all day?

I realize that each time you turn on the AC, it spikes in energy because the machine needs to fire up again, but wouldn't leaving it on charge up a huge electricity bill as well?

I always switch the AC to economy mode when I leave the apartment rather than turn it off if I'm only outside for 1 or 2 hours.

As for leaving the AC on for longer than 2 hours...wouldn't it be cheaper to just turn it off?

It spikes for 2-3 minutes at most until it is running at a set temp. So yeah I would turn it off if I didn't need it for a few hours.

If you have it on an auto setting, it will take longer as it attempts to cool until the temp set. But then it will fluctuate the power drain up and down (spikes) as the ac unit attempts to hold that temp setting.

Turn it off. The additional few minutes of start-up is really pretty trivial, and cooling an empty room/house/apartment is simply wasting money. (Just like heating an empty house in winter also uses more energy.) The only reason to leave the A/c unit on is for comfort, not saving money.
(One of my previous jobs was working in retail electricity so I learned some things about how appliances use energy.)

This has been a popular topic in Japan for the last few years. The bottom line is: it depends on lots of factors (like temp outside, room size, insulation, efficiency of A/C, etc.), but for a shorter outing it is more economical to leave A/C ON.

Watch this TV program: https://www.youtube.com/watch?v=NAockM0wxqY

In above specific house where the experiment was conducted:
On a cloudy day, it's more economical to leave A/C ON if you are out of the house for 1 hr 16 min or less,
On a sunny day, it's more economical to leave A/C ON if you are out of the house for 5 hr 27 min or less.

Thanks Ray, I will check out this TV program.

Thank you for the replies.