A capacitor is a device that helps the compressor and motor start and run efficiently. A “dual run” capacitor is simply one that has two capacitors in the same housing. Capacitors work extremely hard, cycling on and off thousands of times every second the compressor is running. When your compressor runs more than normal because the weather is unusually hot, that means your capacitor’s life span will be shortened. A capacitor can also go bad if the voltage in your home varies. This can literally cause a capacitor to expand like a balloon and then pop.
It is very important that you call a professional if you have a capacitor problem. If it is not the exact same rating as the one that needs to be replaced, your air conditioner’s motor may stop working completely.