I received a weekend emergency call during an unseasonably hot September day because the customer's air conditioner had stopped working completely, with the outdoor unit just making a low humming noise. I immediately identified the symptoms of a failed capacitor. After safely disconnecting power, I tested and replaced the bad dual-run capacitor with a new one matching the exact specifications. Upon restoring power, the compressor and fan started up immediately. The customer was extremely relieved to get their AC working again so quickly, especially since they were expecting guests that afternoon.