I was dispatched to a residential home for a unit that was not cooling. Upon arrival, I found that the compressor was not running. I checked the capacitor and found that it was not working. I replaced the capacitor with one on the truck and the unit started up. I then hooked up the gauges to read the refrigerant pressures and found that the system was low on refrigerant. I added 2 pounds of 410a to the system and the unit is now up and running.