Why Do My Lights Flicker When the AC Comes On?

It’s a completely normal occurrence for your lights to flicker when the AC turns on … most of the time. There are some key exceptions, which can be signs of a more serious electrical or HVAC issue. In this guide, we’ll break down why this mysterious occurrence happens, how to know when it’s a problem (and when it’s not), and how you should respond.

What Happens to Your Lights When the AC Turns On?

Lights flicker when your AC turns on because electricity is pulled away from them momentarily to support the enormous power draw required to turn on your air conditioner. It’s likely not a severe problem, and it’s certainly not a spook or spirit trying to get your attention. This reaction is common, particularly in older homes where electrical panels aren’t equipped for modern AC units.

Flickering lights when your AC turns on are okay if:

• They only flicker for a split second.
• They only lose a small percentage of their brightness.

A flicker lasting a fraction of a second is a common reaction when an AC turns on. Likewise, if the lights don’t go entirely out but only dim slightly during that short moment, then you’re probably in the clear. 

It’s completely natural to be a bit spooked by flickering lights. You’re not losing your mind or overreacting. Your eyes are simply doing their job. Most people can detect 10 to 20 flashes of light per second, sometimes more. So, if your AC startup draw is only one-tenth of a second, there’s a good chance you’ll see it because your eyes are capable of doing so.

How to Know if Flickering Lights When Your AC Turns on Is a Real Problem

We’ve determined that it’s normal for the lights to flicker when the AC turns on and that we will notice when it happens. Now, it’s time to understand what’s NOT normal.

Key signs that flickering lights when the AC turns on are a real problem:

• Lights turn on and off rapidly and repeatedly when the AC turns on
• Lights lose almost half of their brightness
• Crackling or sizzling sound accompanying the dimming of your lights, or the lights go out completely (even for a brief moment) when the AC turns on

Lights turning on and off rapidly is a sign of damaged wires. Damage, such as discolored or charred wiring, can cause a loss of electrical current to your lightbulb. This, in combination with the temporary voltage drop that happens when your AC turns on, could cause your lights to dim or flicker more significantly than usual. If you suspect your wiring may be damaged, call right away to have a professional inspect the problem.

Lights losing almost half of their brightness is a sign of a broken or weak AC capacitor. The AC capacitor is what gives the AC an extra energy boost to start. Over time, capacitors can lose their ability to store power. When this happens, the AC draws additional energy from other appliances to start. It’s normal for your lights to dim 3% to 5% when your AC unit begins, but if you notice them dimming more significantly than that, you should call a professional to have your capacitor inspected.

Crackling or sizzling sounds accompanying the dimming of your lights or the lights going out entirely means you may have an overloaded circuit. Ideally, your AC should be on its own circuit to enable it to run safely. But sometimes, it’s hard for homeowners to tell how their homes are wired. And it’s not uncommon to see other appliances on the same circuit as the AC, especially in older homes. Overloaded circuits can cause fires or electric shocks. If there’s any concern or confusion regarding your home’s wiring, have a professional inspect your circuit breaker. 

When in Doubt, Get It Checked Out

It can be hard to decide what looks and feels “normal” when you experience something as odd as flickering lights. It’s a natural reaction to not only notice but be a bit spooked by it. Most often, if it’s a split-second flicker that hardly dims when the AC turns on, then you’re part of the vast majority of homes with no problem. But if you have even a shadow of a doubt or aren’t sure what to make of it, it’s best to schedule an inspection with a professional.

Call (330) 753-7711 or contact us online to schedule an inspection.