The best way for checking air conditioner fuses, to check the cardboard fuses, is with either a continuity tester or an ohmmeter. An inexpensive continuity tester costs around $5. Both instruments will verify if the fuse is good or not. Air conditioner not working article.
You can’t tell if the fuses are bad in the basement or in the box outside. They are cardboard tubes with copper ends. Fuses do not necessarily wear out, either they are good or not. It is a good idea to replace both of them and save the old good one as a spare.
When purchasing fuses for an air conditioner, or any motor operated appliance, get time-delay fuses. A time-delay fuse allows a few seconds before it goes. That short bit of time allows the motor to get up to speed.