Capacitor Failings

Common questions we get when a capacitor needs to be replaced is..

  • We just had that replaced, why did it fail already?
  • Why all of the sudden are my capacitors failing?
  • Until recently, I have never had to replace my capacitors?

A podcast channel I like listening to, recently discussed what commonly cause capacitors to fail. HVACschool.com

Short #77 – What Causes Capacitors to Fail?

After listening to this episode I wanted to share Bryan Orr’s explanation. Great reminders and a couple points I didn’t know myself. I’m always happy to learn more about something I been working with for years.

What actually causes capacitors to fail?

  • Over voltage
  • Over temperature
  • Poor manufacturing practices

In it’s simplest of terms, what is a capacitor?
Capacitor stores and discharges every time there is a cycle change. Kind of like a battery, but it’s a battery that stores and discharges really really quick.

When a run capacitor fails you have no current on the start winding.

Common misconception: There is something the motor can do to cause the capacitor to fail. The motor is failing and thats what caused the capacitor to fail.

Actually, the capacitor failed which has no hurt the motor. Failing capacitors are bad for motors, not the other way around.

There are two main reasons a capacitor fails.

  • Overheat: Running hotter than they should be. Not meaning they are running hotter than they are designed, but running hotter longer. The hotter a capacitor runs the shorter its life will be.
  • High Voltage: Not just power surges, but also lighting strikes can cause high voltage. Not direct lighting strikes, but high voltage events.
  • Poor Manufacturing: Capacitors are made of foil and oil. Thin foil plates or sheets are weak and crack easily. Types of oils that dissipates heat and amount of oils used. Try to design right to the spec.

Bryan mentions a brand of capacitors that we have started using more and more of recently. The cost of the capacitor is more, but with a 5 year warranty. It saves the customer multiple visits and cost over a 5 year period. The brand of capacitor’s are the Amrad Turbo’s. There are other company’s also doing that.

What are some things we can do as a tech to help the capacitors?

  • Use metal strap instead of a plastic strap.
  • Position of the capacitor. Positioning them upright unless manufacture says other wise. If the capacitor is designed with enough oil. The position of the capacitor will determine how well it performs by it position.
  • Try to prevent the unit from over heating.
    • Clean the unit/coils to help reduce the storage of heat
  • Reduce the chance of high/over voltage with a surge protection device

Hope you enjoyed this information and the podcast. These are things that our technicians keep in mind as we service and inspect your HVAC system.

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