Why Do My Lights Flicker When My AC Comes On?

If you’re looking for an answer to this question, you’re probably wondering whether this is normal or problematic.

Well that depends. To answer this question, ask yourself these 2 questions:

  • Do your lights flicker only for a second when the AC starts but then the lights immediately go back to normal? If so, this is normal.
  • Do your lights turn on and off rapidly or dim substantially when the AC runs? If so, this is not normal.

So why are flickering lights normal?

Your lights should flicker some when the air conditioner comes on because your AC unit requires a lot of electricity at start up. So when it starts, it’s temporarily pulling electrical power from other circuits in your home.

We’ll go over some of the problems that can cause your lights to dim or turn on and off rapidly and what you should do to fix it. 

But first, let’s take a closer look at what’s happening under normal, safe circumstances.

What causes my lights to flicker some when the AC starts?

Your electrical company delivers a limited amount of power to your home. And, usually, your home has plenty of electrical power to go around.

But when larger, motor-driven appliances (like your air conditioner) start up, they need around 3 to 8 times more wattage. So they have to temporarily “borrow” electricity from other appliances that are currently in use.

This temporary borrowing explains why it’s normal to see your lightbulbs flicker when the AC comes on.

Now let’s look at a few situations where that interruption of power is not normal...

What does it mean if my lights turn on and off rapidly or dim when the AC starts?

You may have a more serious electrical problem if you notice:

  • Your lights dim when the air conditioner starts
  • Your lights turn on and off when the air conditioner starts (much slower than “flickering” pace)

These situations often happens because of one of these reasons: 

You have a damaged or weak capacitor.

Symptoms: Your lights dim (especially if they lose around 30% to 40% of their brightness).

What to do: Replace your capacitor. 

Your capacitor is basically a big battery that provides the extra burst of power your AC motor needs to kick on.

Over time, your capacitor loses juice and needs to be replaced. So, if your lights are losing a good amount of their energy and dimming when the motor kicks on instead of the normal flicker, it’s a sign that the capacitor is losing strength and isn’t providing enough power to kick start the motor. So, it pulls more energy than it should have to from the lightbulbs and other running appliances.

Your AC isn’t on its own dedicated circuit.

Symptoms: The lights turn on and off or just turn off completely. There may also be a buzzing/crackling sound when the AC comes on. The circuit breaker may also trip.

What to do: Have an electrician inspect your electrical wiring/circuits in your home and provide safer circuit options. All major appliances should be on their own dedicated circuit that provides the exact amount of wattage it needs to run. If it shares a circuit with other appliances, the amount of current the circuit draws will likely be more than the wiring is designed to handle. Eventually, this can cause the breaker to trip or worse, cause an electrical fire from overheated wires.

Related: Air Conditioner Keeps Tripping the Circuit Breaker? A Minnesota Tech Explains

You have damaged/loose wires. 

Symptoms: Lights turn on and off. Light bulb wiring may be ashy, charred, burnt, etc.

What to do: Have an electrician inspect your home’s wiring for damaged wires and repair/replace them. 

If your lights have an existing loose connection, it's probably already suffering from a voltage drop. And then, when the AC kicks on and borrows more power, it may totally lose power for a second or two. If the loose wire is close to the AC motor, the rapid turning off and on may also be due to vibrations from the motor.

Think you need a MN electrician?

If your lights do anything other than flicker briefly when your AC starts, you could have a more serious electrical problem on your hands.

Don’t wait to get it looked at.

Schedule your appointment with On Time Service Pros today to get this problem fixed as soon as possible.


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