Informational Guide

Lights Flicker When AC Turns On (How To Fix DIY)

by jtanner

It is no secret that air conditioner units draw a lot of power, especially on start-up—as one of the largest drains on our electrical supply, keeping your home cool is a necessary evil. When your lights flicker when the AC turns on, though, it can cause panic or worry.

Do you need to call a professional electrician or HVAC tech, though? This guide will look at all the possible reasons for the light flickering and help you decide what to do. In some cases, you may need a pro. In others, it could be a simple fix you can do in an afternoon by yourself. Let’s find out.

There are a lot of reasons that lights can flicker, and in a lot of those instances, it happens so fast we don’t even register that it happened. When we do notice, though, it can be a reason to panic.

Just because your electricity stutters when a high demand is put on it doesn’t mean it is a bad thing. Older homes may have less connectivity between sources, and a modern AC can cause a high draw that momentarily takes power from other areas to turn on.

If you think there is a problem, or the flickering has only recently started (or gotten worse), you most likely have one of the problems listed below.

Lights Flicker When Turning On AC

Damaged Or Loose Wires

When a technician is called out, one of the first things they will check for is a loose wiring connection. Pests, rodents, and insects can chew through wiring over time or even pull wires out, causing shorts and spotty connectivity. In these cases, the wiring needs to be repaired or replaced. It is also wise to treat the root problem and prevent further infestations.

Pests aren’t always the problem, though. Time, gravity and environmental issues can also be a cause. Over time the wiring can sag, droop or the house can settle an inch and pull on some of the mounted wiring.

Because the wiring can cause sparking in the walls or around insulation, it becomes a fire hazard. A professional needs to be called in to locate, diagnose and repair the problem before it becomes a major issue.

Other wiring, though, is more exposed and maybe a DIY fix. For example, you can remove the front panel on your thermostat and even the cover of your circuit breaker to see if there are any loose, disconnected, or broken wires. Just be cautious inside the breaker panel as it contains 240 volts which is very dangerous.

Checking outlets and plugs in the rooms that go dim can also be a DIY task to help locate the problem area. If you are good with tools and understand how to disconnect power to an outlet, you can pull out those outlets and replace them yourself, if needed.

Damaged Or Weak Capacitor

A run capacitor has the dubious job of supplying that high power to the compressor to get it started. A capacitor works much like a battery. It stores electricity while the system is running. Once your AC shuts off, it requires more than the supplied energy to start again.

When the signal comes from the thermostat, the capacitor unleashes its stored energy to give that jolt needed to the rest of the system.

Over time, though, the capacity of the capacitor, much like a battery, will diminish. The capacitor can go bad, swell, and stop performing as expected. When this happens, the AC will draw power from other sources connected to the circuit breaker to get that jolt of power.

The result of a capacitor going bad is dim lights for a moment (up to 5% dimming) and flickering of lower voltage lamps, appliances, or devices. While you can replace a capacitor as a DIY project, it is best to hire an HVAC technician to diagnose the capacitors and check for other issues that could cause them to fail.

Overloaded Circuit

If you open the door on your circuit breaker panel, you will see several breaker switches. Each one of these is connected on the back side to the main power supply to the home (240 volts).

Each breaker represents a single circuit in your home. For the most part, you will have at least one breaker for each major area of your home. The bedroom lights and outlets will be on the same circuit, the living room will have a circuit, and your kitchen may have one or two circuits as well.

On most installations, the HVAC system will take up two circuits, and nothing else will be connected to them. In some instances, though, depending on install location, those circuits can also connect to lights or outlets in a nearby room.

If this is you and those lights or outlets flicker when the AC kicks on, it is just drawing power from the circuit that the lights are also on. You can quickly fix this issue by changing where your lights are plugged in.

For hardwired lighting, though, you will need a professional electrician to run a new circuit for those outlets and lights that are not connected to the HVAC system.

Maxing Out The Distribution Panel

The distribution panel (Circuit breaker panel) works a lot like the fuel tank on your car. It holds all of the power coming into your home and distributes it to the required areas of your home. Like that fuel cell on your car, though, it can only hold so much electricity or fuel.

While your gas tank only supplies one line of gas to the engine, the distribution panel feeds many lines. When that limit supply is called on to start an AC system, it can cause light flickering as it pushes the power supply to the high priority area.

If this is the case in your home, you need to call a professional electrician to install a larger capacity distribution panel. In most cases, they will also split some of the larger circuits into smaller ones, giving you more breakers and better control over the power distribution in your home.

Can My AC Unit Cause a Power Outage In The Home?

The short answer is that, yes, your AC unit can cause a power outage in your home. This isn’t always the first cause for alarm, though. In almost every case listed above, the problem is a quick and temporary issue that is normal and part of the AC operation process.

Some can be fixed; others are expected. However, if the distribution panel is getting overloaded, it can cause a complete power outage to your home. When a smaller circuit panel is overloaded, the jolt needed to start the AC can cause the breakers to switch off.

When this happens, you will lose power to the home and need to manually switch on the breakers once again. The longer this happens, the worse the panel will get, degrading to the point where it won’t supply power to the breakers, or the breakers themselves will char and burn out.

On top of tripping breakers and causing a power outage, repeated overloads can cause sparking and arcing, resulting in a fire or the need to replace the entire distribution panel and breakers inside.

If your AC system turns on and causes a power outage, you should call a professional electrician as soon as possible to get the situation repaired and upgraded before it becomes a significant issue that can cost you thousands (or more) to replace.

Why Do My Lights Flicker When My Neighbor’s Central AC Turns On?

Flickering lights when the neighbors use their air conditioner is actually a common problem in many areas. It is most common in multi-family housing like townhomes, apartments, and condos, but can also happen in single-family residential neighborhoods.

The distribution panel in your home, as we covered above, has a limit to how much electricity it can hold and pass through. That power is supplied down the line from a transformer that can provide hundreds or even thousands of amps.

Since your home may only require 100 or 200 amps, one transformer can supply multiple homes at once. When the air conditioner next door causes an excessive draw on the supplied electricity, the transformer will change the workload quickly to supply the additional need to that side of the circuit.

When this happens, your home, connected to the same circuit, can experience a power drain, which can cause dim lights, flickering lights or outlets, or even power outages.

If this is your case, you will need to call the power company to perform tests on the transformer, lines, and connections. They should also check all grounding and routing from the transformer to the homes. Their inspection will tell you what the issue is and any possible solutions.

Lights Flicker When Neighbor Turns On AC

Common Lights and AC Unit Questions

Would a bad AC circuit breaker cause lights to flicker?

Yes, if you have a bad, burnt, or disconnected breaker in your distribution panel, it can absolutely cause flickering lights, dimming lights, or power outages. The supplied power to the bad breaker will be routed to other areas, and that rerouting and draw can cause lights in other areas to flicker for a moment.

Why don’t my lights flicker if they receive AC current?

Alternating Current (AC) is not a constant supply of electricity and pulses, or alternates. However, this alternating happens in milliseconds. The truth is that lights, televisions, and other electrical devices do flicker; the human eye cannot adjust quickly enough to notice, though.

Should I contact an HVAC repairman or an electrician if more assistance is needed?

Electricity can be dangerous to work with if you are unfamiliar with the process and safety requirements. When your lights are flickering, or your AC is drawing too much power, it is always a safe route to hire a professional to handle the issue. On top of being able to fully diagnose the situation and handle any needed repairs or fixes, most of their work will also be warrantied, something you can’t get with a DIY repair.

How much would it cost to have someone take a look at this problem?

Electrical inspection services and HVAC inspections will usually come with a flat-rate fee. While some contractors will charge an hourly fee for the actual repairs, the inspection and diagnostics are usually a single fee. That fee will vary depending on your needs and location, but the US average is between $100 and $400 for a full inspection.

Related ArticlePrimer on Air Conditioner Repair

Conclusion

When your lights flicker when the AC turns on can be a situation that causes panic or stress. You may fear losing power completely or worry about a fire or other major repair issue. But, in most cases, the flickering light is a normal situation and nothing to worry about.

However, if the issue is new, gets worse, or the dimming and flickering last longer, it can signify a larger problem. Knowing the cause, how to diagnose and repair yourself or when to call in a professional was the basis for this guide.

Hopefully, you have a better understanding of how your home handles electricity and why the lights flicker when your AC turns on.

Last Updated on January 9, 2023

Top