Commonly refers to a cooling-only air conditioner, as opposed to a heat pump (エアコン).
In summer, I tend to leave the air conditioner on all the time.
General term for a device that cools something, such as a beverage cooler or CPU cooler. Less common than the air conditioner sense.
This cooler can chill cans quickly.
It was hot, so I turned on the air conditioner.
It got cooler, so I turned off the air conditioner.
The air conditioner cools this room very well.
I leave the air conditioner running while I sleep.
room cooler; air conditioner