To check if a pool pump's capacitor is still working, use a multimeter. Before testing or removing the capacitor, discharge it by touching the terminals with a screwdriver. A capacitor is a device that stores electricity and can be found in various electronic devices and power plants. Single-phase motors use capacitors to help them start and for energy savings. There are two main types of motor capacitors - start capacitors and run capacitors. A start capacitor is used to give a motor an extra electrical push to start it turning and isn't used for more than a second or two, while a run capacitor is an energy-saving device that is in the motor circuit at all times. If a start capacitor fails, the motor will not be able to begin turning, while a bad run capacitor can cause various problems such as not starting, overheating, and vibrating. Run capacitors are heavier and more durable than start capacitors since they are always used when the motor is running. Improper current or voltage and overheating due to being used beyond their intended purpose can also cause capacitors to fail.