Lights Dim When AC Comes On

Why do the lights in my house dim when the Air Conditioner turns on?

As we begin summer, the unofficial kick-off of turning on our collective air conditioners has begun. Cringing consumers may dread the electric bill – as utilizing an air conditioner can quickly drive up your utility costs if your home is not properly insulated, as well as other factors related to your air conditioner’s efficiency, age and size of your home.

But, have you ever wondered why when you’re lounging on the couch, with the television and a few lamps on, why the lights suddenly dim when the air conditioner turns on? It only lasts a second, but it’s something that catches you off guard.

What is drawing power in my Air Conditioner?

The two components drawing power in your air conditioner are the compressor and fan. As the compressor utilizes more power to start and maintain than the fan, when combined – the initial startup use of electricity may surprise you.
Digital Thermostat

Let’s assume your air conditioner is rated between 7,000 – 10,000 BTU’s, this means the initial power required to
start your system ranges from 10-20 amps. After startup, the air conditioner operates in a range of 4-6amps. Cost-wise, running an air conditioner at a reasonable setting (68-70F) in a 1500sqft home can range anywhere from 2.30-$3.00/day, (assuming the unit is in operation 6 hours per day) depending on your power provider’s rates.

What makes my lights dim?

start-up capacitor

The need for your air conditioner’s motor shaft speed to get to a certain RPM is what causes the large draw of power. But, if we are looking to point fingers, the real culprit is the start-up capacitor. This gives the motor a boost when tripped by the thermostat.

But, with age, the start-up capacitor can become weak and not operate as efficiently as it had from day one. As the start-up capacitor reaches an extreme point of degradation, you may experience the circuit breaker tripping in your electrical box.

Air Conditioner Do's and Don'ts

Do have your air conditioner serviced every year. Ensure the refrigerant is at its proper level and all components are in proper working order.

Do have an electrician ensure your wiring and electrical panel are properly wired to your local code and in good working order. Cutting corners by utilizing the improper wire gauge or splicing together a damaged wire can result in complete unit failure.
Don’t try to service your own air conditioner. If you do not have an electrical or HVAC background, you could electrocute yourself.

Don’t assume the air conditioner is faulty. An electrician can verify the power consumption required and ensure your incoming service power, electrical panel and wiring are sufficient for the unit you have.

Contact a Professional

If you're still uncertain or are concerned you have an issue - always contact a professional.

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