Dual run capacitors are commonly used in HVAC (heating, ventilation, and air conditioning) units. Dual capacitors have three terminals, unlike regular run capacitors, which have only two. Electrically, they are the same as run capacitors that have two terminals. Using a dual run capacitor allows you to save space if you have a small mounting area. The terminals are also clearly marked, making it easy to hook it up to the different components of your air conditioner.