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Motor Run Capacitors

Motor run capacitors are designed for use with single-phase motors, such as air conditioners, refrigerators, washers, and other similar products. These capacitors run continuously to phase-shift the incoming power in order to engage the winding, creating a magnetic rotating magnetic field. This field provides more torque to the motor and helps keep it running efficiently.

Most motor run capacitors contain a metalized film and oil sealed into a metal case. The oil fills any voids while aiding heat transfer, protecting the film from corrosion and helping suppress degrading caused by corona. These capacitors are available in multiple voltages, including 370VAC and 440VAC, and have between two to four terminals

When to Replace Motor Run Capacitors

Motor run capacitors can last a long time depending on the application and will usually outlast the start capacitor. Here are a few signs to look for to tell if your capacitor is beginning to fail:

  • The motor is running but is drawing a high current.
  • The motor has less torque than it should have.
  • Fuses are blowing after the motor runs for a short time.
  • The case has a bulge or is leaking.

When a capacitor fails, replace it with a capacitor of the same capacitance and voltage. Capacitance, or the amount of energy that can be stored, is measured in microfarads. It is printed directly on the capacitor, usually consisting of a single number or range of numbers followed by either MFD or uF. The voltage rating should at least be the same as the old capacitor. You will also need to make sure that the new motor run capacitor is around the same size as the old one to ensure a proper fit in the housing. Using the wrong capacitor will make the magnetic field uneven and cause the rotor to hesitate, leading to noise and increased energy use with a noticeable drop in performance. The motor will also be at risk of overheating.

For help finding the right motor run capacitor for your application, call 1-800-624-4488 to speak with a product expert today!