How to Know When a Start Capacitor Is Bad

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When the air blows warmer than it should or the normal hum of your machine begins to sputter and clunk, it can lead to worrying questions. When the blower motor capacitor symptoms point to something problematic, it could be a relatively simple fix. The sooner you tackle the issue the easier – and less expensive – it will be.


How to Know When a Start Capacitor Is Bad
Image Credit: Steven Heap / EyeEm/EyeEm/GettyImages

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What Is a Capacitor?

When the compressor is doing its job, the capacitor is cycling on and off at a rate of thousands of times per second. That's a lot of work for a little machine part. The life expectancy of the capacitor depends on the age of the part, as well as how often it needs to do its job, such as daily or annually. The cylindrical part pushes energy to the motor that runs the air conditioning unit. It not only turns it on, which is the woosh sound you may hear when the air conditioning system kicks on, but it also keeps the machine purring while it sends cool air throughout the home.


Why Capacitors Go Bad

If voltage varies, this can be a problem for the capacitor. During peak summer months, the power company may raise or lower the line voltage that leads to your home. This taxes the capacitor and ages it rather quickly. This is also why the capacitor tends to go bad right when you need cool air the most. Summer makes the machine work double time. Air conditioners are connected to high voltage so be careful when taking a look at the capacitor, checking the unit for problems or performing routine maintenance.

Start Capacitor Failure

Motor run capacitor failure symptoms include warm air flowing from the vents inside the home, the air conditioner taking more time than usual to kick on or it turns off before it is programmed to, or there is a constant low hum emitting from the machine that isn't typical. To test for electric motor capacitor problems, you can use a long stick to push on the unit's fan if it isn't on. If the blades spin undeterred from the slight push, you have a start capacitor failure. A professional can replace a faulty capacitator without having to replace the entire unit. If your unit is more than 10 years old, you may benefit from a modern, more energy efficient air conditioning unit and save more money over time. An air conditioner that doesn't have to work hard will easily save you some serious cash.



Kimberley McGee is an award-winning journalist with 20+ years of experience writing for a variety of clients, including The New York Times, Las Vegas Review-Journal Home section and other national publications. As a professional writer she has researched, interviewed sources and written about home improvement, interior design and related business trends. She earned a B.A. in Journalism from the University of Nevada, Las Vegas. Her full bio and clips can be viewed at