Several years ago I waited until the first hot day of summer to turn on my AC. This is how I found out about one of the busiest times for repairmen and had to sweat for two weeks. Now I do a test run a couple of weeks before it heats up. Same goes for the furnace at the end of Autumn.
If you have a portable AC unit don’t forget to clean the air filter(s) before you start using it for the season!