The idea behind capacitors was first discovered in the mid-1740s in Germany. Ewald Georg von Kleist realized that he could store an electric charge by connecting a volume of water with a high-voltage electrostatic generator. Over the course of multiple centuries, the technology for capacitors has evolved in leaps and bounds, but the concept is basically the same. Capacitors are designed to contain an electric charge, including multiple pairs of conductors, which are broken into different parts by an insulator.
Any cooling or heating system in your house with a motor will require a capacitor to function properly. The size of the motor in your system is the determining factor of the size of your capacitor. The most widely available capacitor sizes are 10, 7.5, and 5 mfd. These sized capacitors are generally inexpensive, but usually correspond to motor failure within days after being replaced.
The two main types of capacitors are single run capacitors and dual run capacitors. There are also start capacitors, which give the compressor an extra boost of energy when the motor starts up. Unlike start capacitors, which only give that brief boost, run capacitors work continuously while the motor is powered. Run capacitors are usually made of polypropylene film, allowing them to remain energized during prolonged periods of running.
Single run capacitors mostly function as parts in small air conditioning units. They can be hooked up to a single motor due to their two connections. There are few disparities between dual and single run capacitors. Basically, a dual run capacitor is two run capacitors in one. Other than being vastly more powerful than single run capacitors, there is virtually no difference between the dual and single capacitor. Dual run capacitors are used in bigger AC and heat pump units. They also have three connections. When you have to replace a capacitor, knowing how many connections the previous one had will be the best way to determine whether you need a single or dual run capacitor.
On many occasions, it might be in your best interest to bring in a professional technician with the proper tools and knowledge to determine whether or not there are issues with a capacitor. Deteriorating capacitors start to affect the motors they help operate. As it gets worse, the motor may stop working completely. Some capacitors appear swollen when they start to fail and can even burst if not replaced before the swelling continues to increase. Newer capacitors have a “Pressure Sensitive Interrupter”, which prevents swelling by making the capacitor fail before it reaches that point. The extent of the damage will also determine whether the capacitor needs to repaired or replaced.