What Is an Air Conditioner Hard Start?

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Ka-chunk ... ka-chunk ... ka...chunk! You know that sound your car makes when you try to start it and the battery is almost dead but not quite? Well, if an air conditioner had the same kind of motor, it would make the same sound when it has trouble starting. It's called a hard start, and the reasons it happens to an air conditioner are pretty much the same reasons it happens to a car: There isn't enough electrical power available to wake up the engine, or the engine is toast.

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In a car, the starting power comes from the battery, but in an air conditioner, it usually comes from a capacitor — an electrical component that stores energy and makes it available when the air conditioner's compressor needs it. If the start capacitor on your air conditioner is worn out or if one wasn't supplied with your unit, you can have a technician install a hard-start kit, which includes a new capacitor. However, it's also possible the compressor is just worn out, in which case you should replace the air conditioner just as you would replace a car with a worn-out engine. Here's a closer look at hard-starting air conditioners and what to do if your AC unit has a hard start.

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Why an Air Conditioner Needs a Capacitor

The compressor is the heart of an air conditioning or heat pump system, and it's basically a pump with lots of moving parts, some of which rub against each other and create friction. When it starts, it draws four to eight times the amount of electricity it does when it's running. That's a lot of power, and it can seriously tax the electrical system. The situation is analogous to riding a bike: You have to exert a lot of strength to get going, but once you're up to speed, you can settle back and keep going with much less energy expenditure.

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A start capacitor stores energy and releases it all at once, giving the motor the jolt it needs to wake up from its resting state. Once the motor starts running, it has momentum and will keep going on much less power, although most units also have run capacitors to keep things going smoothly.

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Symptoms of a Hard Start

An air conditioner motor is electric, so it won't make the same thumping noises a car engine makes during a hard start. It will display a few telltale symptoms, though, and these do include noises:

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  • The compressor starts and then shuts off immediately.
  • You hear clicking noises when the A/C is starting up.
  • The circuit breaker trips when the A/C cycles on.
  • The lights flicker. A small amount of flickering is normal, but noticeable dimming is a problem.

Not all of these symptoms are due to capacitor malfunctions, and installing a hard-start kit may not be a remedy. An HVAC technician will be able to determine that.

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When Installing a Hard-Start Kit Makes Sense

When a technician inspects your compressor, it may turn out that internal parts are rusty and just need to be lubricated. If that solves the problem, you don't need a hard-start kit. However, if your A/C unit is old and the compressor is wearing out, a hard-start kit may give it extra life, but replacing the unit will probably be necessary at some point not too far down the road. On the other hand, the problem might be a worn-out capacitor, and if that's the case, replacing it is definitely worth the effort.

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If you have a new air conditioner that's hard starting, it probably doesn't have a start capacitor. Some manufacturers don't supply them with new units. If that's true, you need a hard-start kit. It will prolong the life of the unit and save energy.

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