Run capacitors used in HVAC applications can be either round or oval shape. They also can be either a single or dual capacitor. A single capacitor has one set of plates and is used for the operation of one motor. A dual capacitor is actually two capacitors in one shell sharing a common plate. Dual capacitors are used for the operation of two motors. The two different type of capacitors can be differentiated by the terminals on top. A single capacitor will have two terminals and a dual capacitor will have three terminals on top. The two internal capacitors share a common plate for both motors labeled C on the top of the capacitor. The other terminals will be labeled FAN for the fan motor and HERM for the compressor. It is very important to make sure the wires go back on the same terminals when replacing a capacitor. A capacitor can fail and cause the fan motor and compressor not to start. The top of the capacitor should be perfectly flat. If it is slightly domed or has any type of oil leak it should be changed. Bad bearings in a fan motor can cause a capacitor to fail. Capacitor failures are very common during heat waves as excess heat does cause damage. Make sure power has been disconnected before making any repairs. In the picture below the capacitor on the right is slightly domed. Notice the flat top on the new capacitor on the left. Also notice the terminals are clearly marked.