Why Do The Lights Dim When AC Turns On? | How to Find the Problem

Are you wondering why do the lights dim when AC turns on? Flickering lights from time to time may not be a problem. But if this happens on a regular basis, you need to do something about it. There are a number of reasons why your lights may flicker whenever you turn on the AC unit. Knowing them is essential to keep your lights and AC running smoothly and repair any damage as soon as possible.


lights dim when AC turns on

Reasons Why Lights Dim When AC Turns On​

When the lights get affected by an AC unit, it can be caused by one or more reasons. These can be easy to fix alone or warrant the need to call for the help of professionals. Knowing the cause of this problem is crucial in determining a solution and making repairs whenever necessary.

Faulty Electrical Connection

The most common cause why lights end up flickering with an AC being turned on is due to faulty electrical connections. Wirings may have become damaged through a variety of reasons. Some may have been cut or exposed through wear and tear, rodents chewing on the wires, or getting burnt out. Identifying the part where the connection is disrupted is important in order to make repairs in the right areas.​

If you’re handy with wirings and observe proper safety measures, then you can make repairs yourself. Most of the time, it’s easy to wire a 3-way switch or even a wire a 4-way switch. But if you don’t have enough experience handling electronics, it would be better to hire a contractor instead.​

Faulty Electrical Connection

Capacitor Problems

The capacitor serves as the battery of your electrical devices at home. When it gets weak or damaged, it can’t handle the power that your appliances draw out. This gives electrical devices that use a lot of power such as an AC unit to take away electricity from other sources such as the lights.

This leads to flickering and dimming at around 30% to 40% depending on capacitor’s remaining strength.​

There’s no real easy way to handle this. You either have to call a professional to fix your capacitor or replace it entirely. You should consult first with a contractor to see if your capacitor needs a repair or a replacement. Once done, you can expect your lights to be brighter even when your AC is running.

Overloaded Circuit Breaker

If you hear a crackling noise along with your dimmed lights whenever you turn on the AC unit, you might have a problem with the circuit breaker. When multiple appliances are connected to a single circuit, there are times when the circuit breaker gets overloaded.

This usually happens in old homes with circuits that can’t handle the demands of new air conditioning units or homes using high-voltage appliances.​

When the circuit is the problem, consider it to be an emergency. This can cause electric shock or even start a fire if left ignored. One quick solution is to unplug appliances that are using the same circuit as your AC unit to prevent overloading.

But for a more permanent solution, you need to work with a professional to either establish another separate circuit for your AC unit or reduce the number of appliances in your home.​

Overloaded Circuit Breaker

Pushing Power Supply Too Much

A home can only provide so much in terms of power. If you use a lot of electrical appliances on a regular basis, you can expect something to falter overtime. This includes lights getting dimmer whenever you turn on an AC unit.

This maybe because you’re pushing your home’s power supply too much. You’re using too much power that your home can handle giving, leaving certain areas lacking.​

Doubling down on your use of appliances or managing power consumption is a quick and easy way to fix this. For example, you can turn off the electrical heating in your garage when not in use if you turn on the lights and AC inside the house. This allows your other appliances to draw out enough power without straining the available supply.​

Things to Remember When Making Repairs

It’s tempting to make repairs yourself when you have an idea of the cause of this problem. However, always take into account your experience in handling electrical equipment and your safety.

If you have little to no experience at all, then consider hiring a professional instead. This will let you:​

  • Prevent further damage to electrical equipment
  • Prevent electrical accidents
  • Prevent from making a potential fire hazard
  • Save time and money


There are many possible causes why your lights dim when AC is turned on. It can be a problem with the wirings, the capacitor, the power supply, or maybe even the circuit. Having skills in electrical equipment such as wiring light switches can also help resolve this problem yourself. However, pinpointing the problem is a key element in order to make the necessary repairs, be it by yourself or hiring professional help.


  • Emma Clark

    Hi there! My name is Emma Clark, a part-time interior designer, house flipper, and full-time mom. This blog is the fruit of my extensive experiences as an interior designer and home improvement enthusiast. More so, I'm here to share with you a lot of great ideas on what you can do to make your home into a masterpiece: all cost-effective and amazingly creative.