Things always go wrong with your A/C unit when you need it the most. Usually when it’s 90 degrees plus outside.
One of the biggest problem is a faulty capacitor. The capacitor is located in the control panel in the condensor unit. It looks like a small “Red Bull” drink aluminum can. You can usually tell it is damaged just by looking at the top of the capacitor. All capacitors have a receeded top with wires connected. If you see some bloating, this is more than likely damaged or will need to be replaced soon. I always check mine first when I’m having issues with high temps, the fan not running, and or the handler unit always running.
This is good to know for your personal system and easy to replace. I don’t recommend adding this to your list of things you can service for your customer unless you are licensed.