YSK because the first hot spell is when most people discover their AC unit is broken.
Several years ago I waited 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.
Edit to add: YSK line (Rule 2)
It was probably running R-22 which you can still get but it isn’t manufactured anymore. It’s ozone depleting so all production and import of the stuff was completely banned in 2020 and it has been in the process of being slowly phased out since 2004. The only source for it is stuff recovered out of other systems or any existing stocks which are running out very quickly. That means it gets more expensive every year. Now a days most HVAC companies will just replace those systems rather than fixing them for that reason.
Also it’s become very expensive compared to the new stuff for this reason. Like over 10x more expensive per pound.