Addressing a no-start issue on an existing HVAC unit, I began by inspecting the electrical disconnect for any visible signs of damage or failure. Using a multimeter, I confirmed the incoming voltage supply was within acceptable parameters. However, the disconnect's fuse cartridges had failed open due to an overcurrent condition. To restore operation, I replaced the cartridges with new 40-amp Fusetrons properly rated for this equipment's maximum overcurrent protection device requirements per NEC code. After verifying all electrical terminations were secure, I successfully energized the unit and closely monitored operating amperages to validate the system was functioning normally without any lingering fault conditions.