Why Does My AC Just Hum and Buzz, But Doesn’t Turn On? A PHX Tech Explains.

Here’s the situation: Your AC thermostat clicks on but only warm air is coming out of your vents.

You check your outside unit and notice that the outdoor unit is humming like normal but the fan isn’t spinning and is making a buzzing noise.

So, what exactly is the problem?

If your outdoor AC unit is humming but the fan isn’t running, that most likely means you have a bad fan capacitor.

Thankfully, there’s a short-term fix that’ll keep you cool until you get your capacitor replaced. We’ll show you that cheap trick in a bit. But first, let’s take a look at why capacitors are so important in the first place.

A capacitor is a small, cylinder-shaped metallic object that sits on the side of your outdoor unit. It acts like a battery and stores large amounts of energy.

In the case of air conditioners, capacitors are used to kick-start the compressor, the outdoor fan motor, and the blower fan (indoor unit fan).

You see, large appliance motors require up to 5 or 6 times more energy at startup than they require when running continuously. Capacitors offer that extra jolt of electricity needed to get motors started and/or to run continuously.

Just like a battery, capacitors will weaken and lose the ability to hold an electrical charge over time. They’ll also have a shorter lifespan if they suffer some sort of damage, like from high temperatures or high voltage.

Some visual signs of a bad capacitor include:

• A swollen, “mushroomed” top
• A capacitor that is corroded or rusted out on bottom
• Fluid leaking from any part of the capacitor

So, if the capacitor connected to your fan motor goes bad, the fan will fail to start. And this prevents your unit from moving the heat from inside your home to the outdoors (which explains why the air coming from your vents is warm instead of cool).

Need a quick fix for your failed fan motor capacitor?

Turn on the AC unit and take a long, thin object (a stick or screwdriver will work fine) and use it to push the fan blades inside the compressor.

This should provide the “kick” the fan motor needs to get up to speed. Please be sure to take safety precautions when doing this so that nobody gets hurt.

Note: if this doesn’t get your fan running, you most likely have a bad fan motor and will need to have a professional replace it.

If the capacitor connected to your fan motor is weak or has finally died and won’t start your fan, you need to have a professional replace it as soon as possible.

Why?

When a capacitor fails, the motor it is connected to will still try to come on. And most of the time, the motor won’t be able to start on its own. This stalling can cause the motor to burn out and need expensive replacement soon.

The sooner you are able to replace the capacitor, the more money you will save yourself in the long run.

Note: Although it is possible to replace a capacitor on your own, we don’t recommend it unless you have experience working with the electrical components of your air conditioner.