Why Do My Lights Flicker When AC Turns On? 4 Causes And Fixes

lights flicker when ac turns on

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It’s easy to get worried when there might be something going wrong with your electrical system, and something as noticeable as your lights dimming or flickering just because your air conditioner turns on can definitely be a bit scary.

But is there really something wrong? Is it something you need to worry about or have fixed? Let’s find out, in brief this informational article.

Why Do Your Lights Flicker and Dim when the AC Goes On?

Before we answer this question, we should say that in almost every case there’s nothing to worry about – flickering or dimming of your lights is pretty normal in this situation!

You see, an air conditioner uses a lot of electricity – we don’t have to tell you that, though, if you’ve been paying your utility bills! And in fact the electrical usage really surges when thy AC first turns on, causing everything else in the house to kind of brown out for a moment.

Of course you may not notice this with other things that are plugged in, like a computer or a refrigerator, but it’s quite easy to see with lights, which dim for a moment when the AC starts up and its electrical usage spikes.

Should You Be Concerned?

Again, normally there is no actual problem, and nothing to be worried about. We do want to be pretty clear about this, because we notice that some of the other articles treating this subject can be a bit frightening, with pictures of electrical fires and scary descriptions of worst-case nightmares.

The thing is, these articles tend to be written by electrical companies and air conditioner servicing centers – not to sound cynical, but yeah, they can charge a hundred bucks or more just to come out and check, and will almost certainly say “there is no actual problem.” 

Oh wait, we just said that!

That said, there can be, in some cases, a few reasons to worry – or at least have things checked out, so let’s look at some causes.

What Specifically Might Be Wrong?

Start-up Surge

Like we’ve already discussed, the main and normal reason your lights flicker or brown out momentarily when your air conditioner starts up is that the AC needs tons of power at that moment. It draws what it needs, then its electrical consumption drops to normal and everything is fine.

Faulty Wiring

Do your lights not just flicker momentarily, but continue to dim or darken for an extended time?

If you are noticing not just a surge, but a long-term brown-out, often for the whole time the air-con is running, you may have some problems with your wiring.

You may have shorts, loose connections or damaged wires, and sometimes this can even be dangerous. And while we can complain about what electricians charge, and reassure you that everything is probably fine, if you really think the lights are staying dim it may be well worth the money to have a qualified expert come to your home and check things out.

If there is a problem, you can have it fixed before it gets worse, and if there isn’t, well, at least you’ll know!

Insufficient Wiring

Similar to the last problem, what we mean here is that the wiring system itself may not be damaged or faulty, but just not heavy-duty enough for your air conditioner. 

This may especially true if your home’s wiring is older, or if you installed the AC yourself without an electrician, and some signs this may be the case include more extended dimming of the lights – again, not just a momentary flicker – or especially blown fuses or tripped circuit breakers when the AC starts up or is running.

And again, like with faulty wiring, this can be dangerous, and should be checked out by a qualified electrician – who may well, and rightly so, suggest a dedicated circuit for larger air conditioning units.

Air Conditioner Capacitor

If you notice a kind of mechanical clicking sound in your AC unit when the flickering lights are occurring, or when the AC is starting up, this could be a sign of a faulty air conditioner capacitor. You may also notice that the dimming of your lights happens for longer than just an instant or is pretty significant.

The capacitor stores electricity, and gives it to the AC motors during start-up to compensate for the huge surge in electrical consumption, and if it fails it can cause real problems, eventually burning out the motors.

So again, although we would love for you to be able to save money and avoid pricey service calls, if the capacitor needs replacing it’s much better, and much cheaper, to do it sooner rather than later!

So, Didn’t We Say Something in the Title about Fixes?

We should be pretty clear here, because we ourselves are avid and enthusiastic DIYers, and if there is a problem we can fix ourselves we’re all over it!

But if you are having electrical problems, especially major ones which might involve worn, broken or damaged wiring, or the need to have heavy-duty dedicated circuits installed, you don’t want to mess with it yourself.

Ok, if you’re like us, you may “want to,” but you definitely shouldn’t, and so by “fixes” we mean have it fixed, not fix it yourself!

Working on electrical wiring yourself can be illegal, or against local building codes, can cause problems with your home’s valuation and even your mortgage and possible future appraisals and financing, and can be very, very dangerous.

And while replacing an air conditioner capacitor may be a bit safer on various levels – following proper safety procedures, of course – it isn’t the simplest job, and any problems you may have might end up being much more expensive in the long run.

So don’t jump the gun – again, in almost every single case the flickering you are noticing is absolutely nothing to worry about, and there’s actually nothing to fix.

But if there is a bigger problem, using a licensed and qualified electrician, or HVAC technician, may be the best money you’ve ever spent.


Thanks for reading our article – Why Do My Lights Flicker When AC Turns On? 4 Causes And Fixes – and please check out our website – Know the Flo – for other informative articles, tutorials and buyer’s guides and a whole lot more!


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