Why Do My Lights Dim When My Air Conditioner Turns On

As a homeowner, have you ever noticed that your lights flicker or dim when you switch on your air conditioning unit? You might be wondering what causes this and if it’s a problem with your AC or your home’s electricity. In this article, we’ll answer these questions and provide you with valuable insights.

Understanding Your Residential Air Conditioning Unit

To better understand this phenomenon, think of electricity in your home like the water in your plumbing system. In a similar way, electricity has a limited supply in your home at any given time. Just as water pressure is divided when you flush the toilet while running a shower, electricity behaves in a similar manner.

When you turn on a high-energy device such as a modern AC unit, the initial power draw can put a significant strain on the available electricity. Consequently, this strain can cause your lights to dim. Although flickering lights might seem concerning, it’s actually a normal electrical response to power being redirected.


Now, how can you differentiate between normal dimming lights and a potential problem? If your air conditioner is functioning properly, you will likely experience the following:

  • Lights dimming momentarily
  • Lights losing only about 5% of their brightness

However, if your lights dim for an extended period, flicker rapidly, or only dim on certain circuits, it could be an indication of more serious electrical issues. To understand these issues and when to seek professional help, continue reading.

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Damaged or Loose Wires

Do your lights quickly turn off and on when you start your AC unit? This could be a sign of loose or damaged electrical wires. Faulty wires can result in the loss of current to your lightbulbs. Additionally, when your air conditioner kicks on, the voltage drop can worsen the problem, causing rapid flickering of your lights. If you suspect damaged or loose wires, it is advised to consult your Beaverton HVAC contractor. They can inspect your wires for discoloration, charring, or looseness.

Weak or Broken Capacitor


If your lights lose 30% to 40% of their brightness when the AC starts, it’s likely a capacitor issue. The AC capacitor functions similarly to a battery, providing a boost of energy to power up the compressor motor. Just like a car battery can lose its ability to store and maintain power, the same can happen to your air conditioning compressor.

Consequently, your AC will draw more voltage from other appliances and put additional stress on the compressor when starting up. This temporary power surge can cause your lights to momentarily dim.

Overloaded Circuits

Having overloaded circuits can pose a serious problem. According to the National Electric Safety Code, major appliances should have their own dedicated circuits. If you trip your circuit breaker or hear any buzzing sounds when you turn on your AC unit, it is possible that your circuits are overloaded. In such cases, unplug any household devices connected to the same circuit as your AC unit. This will reduce the risk of fires and electrical shocks. For a long-term solution, it is advisable to consult HVAC professionals for a comprehensive assessment and potential repairs.

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Home HVAC Solutions in Beaverton & Portland

If you’re unsure about the cause of your flickering lights or need professional assistance, don’t hesitate to reach out to the experts. AAA Heating and Cooling, your trusted residential HVAC servicing and installation company, can provide you with the necessary support. We have two convenient locations, one in Portland and the other in Beaverton.

Remember, if you encounter any HVAC-related issues, trust the experts at 5 WS for reliable information and solutions.

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