AC Unit Humming But Not Turning On? (We Have The Answer)

Ossiana Tepfenhart
by Ossiana Tepfenhart

Problems with AC units can be understandably unnerving, especially when they hum without turning on. This is caused by several reasons such as a bad capacitor or broken motor. Whether it be replacing parts or replacing the entire unit, let’s explore what you should do when your AC hums but won’t turn on.

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If there’s one sound that brings comfort to people who are dealing with swelteringly hot heat, it’s the gentle hum of an air conditioner. However, there are some moments where your AC unit might hum, but it just won’t turn on for one reason or another. When this happens, it’s normal to feel a little alarmed. The important thing to know is how to handle it.

If your AC unit is humming but not turning on, the most likely issue you’re having is a broken capacitor. This can be fixed by replacing the capacitor. If you’re unlucky, your AC unit’s sudden “quit” could have to do with a broken motor. In this case, it’s often better to replace the entire AC unit.

Understanding the “why’s” of this problem is just as important as knowing how to fix it. If you’re concerned about being able to use your unit during these tough times, make sure that you read this article. We’re here to help.

Why Is My AC Unit Not Turning On Even Though It’s Humming?

It can be a little strange to see an AC unit that won’t turn on, even when it’s making noise. However, this is actually fairly common when you understand how an AC unit works. In order for your unit to do its job, you will need to have an extra boost of energy to kickstart your unit’s fan.

Without the energy you need to get your fan working, your unit will continue to hum and stall. If left for too long, an un-moving fan can cause your motor to fail altogether. Oddly enough, a failed motor might still make a weak buzzing noise even though it won’t be able to turn on regardless of whether or not you get your capacitor replaced.

A Humming AC Compressor Motor Is Easy To Test

There is even better news, though. As it turns out, it’s actually super easy to test if the problem is your start capacitor or not. Remember, the capacitor is only needed to get the fan moving, not to keep it running. That means it does not need to be there, doing its job, after the motor starts up.

All you have to do to test your AC compressor’s start capacitor is to get a stick or another long, slender, but sturdy object. Then, try to very carefully use it to push-start your AC compressor fan.

If your fan starts spinning normally after you give it a little push, then you know your start capacitor is bad and needs to be replaced. This will fix your AC humming but not the starting issue.

Remember, Safety First!

The very last thing we want to happen is for someone to get hurt while taking our advice. So, if you are going to be putting a stick into a motor to test it, use some common sense.

It is important to remember that once you move the fan, it will start to spin very quickly. So, even if you don’t know the trick is going to work, assume that it will. So, give the fan a quick push and then a very quick pull back.

A Short Term Fix For A Bad Capacitor

Let’s say that it’s 2 AM, you are ready for bed, but your lack of cool air is killing your ability to sleep. You don’t want to have to call an HVAC person right now. You just want the AC unit to work and are open to a short-term solution. There is something you can do for a day or two without harming your AC unit too much. Here’s what to do:

  • Open up your air conditioner to expose the fan. This can be done by opening up a panel with most models. If you don’t know how to do this for your unit, refer to your owner’s manual.
  • Take a long, thin implement and push the fan’s blades. You can use a screwdriver, a straw, or even a pen for this. If your capacitor still has some “juice,” a simple push will be enough to kick-start it.
  • Get your capacitor replaced as soon as possible. Though this can be a quick fix for your AC, you shouldn’t do it more than once or twice. Trying to make this your go-to will burn out your unit’s motor.

The Long Term Fix For A Bad Capacitor

Like with many other tech items, capacitors can and will go bad. It’s just a natural part of a unit’s wear and tear. When this happens, the only thing you can really do is replace it. To do so, you will need to buy a capacitor that is compatible with your AC unit model, remove the dead capacitor, and replace it.

How Much Does It Cost To Replace Your Capacitor?

Professionally-done capacitor replacement will run between $90 and $470, depending on the unit and where you live. If you choose to do it on your own, you will be able to do it for the price of the capacitor itself. Capacitors can run between $5 and $135 based on the type you need.

How Can You Tell If You Have A Bad AC Unit Motor?

The vast majority of times when you hear an AC unit humming but not turning on, it’ll be a capacitor that doesn’t have the power to kickstart a motor anymore. However, there are a couple of moments when you might have a motor that just happens to be dead on arrival. With these issues, the best way to figure out if the motor is bad is to ask yourself the following questions:

  • Did the capacitor fail a while back, and you just kept using a short term fix? If you kept using a little straw to kickstart your capacitor, there might be a chance that you blew out your motor as a result of all the stalling it did.
  • Did you try the short term fix, only to have it fail? If you tried to kickstart the unit, only to have it fail, it might still be a busted capacitor. However, there’s one single surefire way to figure it out…
  • Did you replace the capacitor, only to have the problem persist? If so, it’s most likely a bad AC unit motor and you will need to get it replaced. It’s worth noting that you can have a motor fail, even if the capacitor didn’t fail first. So don’t blame yourself if it happens.

How Do You Repair A Bad AC Unit Motor?

If you have a bad AC unit motor, then you’re going to have to call a professional in most cases. The reason why is because you have to determine if it’s actually worth saving the unit at all. Depending on what else is wrong (as well as the age of the unit itself), you might be better off replacing the entire unit.

With that said, if you are attached to your AC unit for one reason or another, you can always replace the motor. However, this is usually a sign that you should look into replacing your unit altogether.

How Much Does It Cost To Repair A Bad AC Unit Motor?

Unlike a compressor, which could be a reasonably inexpensive fix, a bad AC unit motor will be pretty hefty in terms of price. This repair can cost between $100 to upwards of $700 depending on the unit. If you have multiple problems with your unit, it may make sense to pay $3,900 to $5,000 to replace your entire unit instead.

How Do You Prevent An AC Unit Capacitor From Going Bad?

With many types of things, an ounce of prevention can be worth a pound of cure. When it comes to your unit’s capacitor, much of its ability to function will deal with age. However, there are still a couple of things you can do:

  • Don’t overdo it with the cooling. The harder your unit works, the more likely it is that you’ll get capacitor burnout. To make your capacitors last, go easy with the cooling and invest in energy-efficient cooling methods like blackout curtains and insulation. If you can handle it, keep the thermostat a little higher than you normally would.
  • Consider installing an HVAC surge protector. We all know that power surges from storms (or even just heavy grid usage) can cause electronics to malfunction. This includes your HVAC kit. To make sure that your system doesn’t suffer from a surge, consider getting a surge protector for your HVAC system.
  • Don’t use your air conditioner when you don’t need it. The less you use your AC unit, the less stress you place on your capacitor. It’s just that simple.

Related Questions

How long does an AC unit capacitor last?

Every AC unit will have a different lifespan for its capacitors, especially when it comes to the varying levels of use that you should expect to get out of them. Thankfully, most capacitors are fairly durable. That’s why you should expect an AC unit’s capacitor to last around 20 years with top quality use and maintenance. With regular use, that number dwindles down to six years.

Can you run an air conditioner with a bad capacitor?

While you could potentially run an air conditioner with a bad capacitor, as long as you do a short-term fix, it’s a very bad idea. This will lead to extreme strain on the rest of your air conditioning unit’s system, which in turn, will harm your ability to keep it all intact. Depending on how much strain your system is under, you might end up permanently destroying your air conditioner.

Why is my AC unit leaking freon?

If you’ve had your unit for a long time, then you probably are seeing a freon leak as a result of corrosion. Corrosion is usually fixed by replacing parts, though sadly, it’s not always preventable. Another potential reason for a leaking AC unit is the impact that may have caused a tear on some of the tubing. This can happen due to high winds, inclement weather, or just a bad hit to the unit.

How much should I spend on a new AC unit?

There is no “set in stone” price that you have to pay. Rather than worry about the price tag, make sure to look for an AC unit that has high-powered, energy-efficient cooling. If you aren’t sure what kind of unit would work best with your home, the best thing you can do is call an HVAC technician or ask a qualified professional for help.

Can I just replace the outside portion of my air conditioner?

The cool thing about central air conditioners is that you can choose to replace the interior portion or the exterior portion, or both. With that said, most professionals strongly argue against replacing the outside portion of an AC unit alone unless there is a highly unusual situation like weather-related damage. Since you will most likely need repairs on the inside portion too, it’s best to pair them together when replacing them.

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Ossiana Tepfenhart
Ossiana Tepfenhart

Ossiana Tepfenhart is an expert writer, focusing on interior design and general home tips. Writing is her life, and it's what she does best. Her interests include art and real estate investments.

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