Do your lights dim when the AC kicks on
Do Your Lights Dim When the AC Kicks On? That Flicker Isn’t Normal — Here’s Why If you’ve ever noticed your lights dimming or flickering the moment your air conditioner turns on, you’re not alone. Many homeowners see this and assume it’s “just how ACs work,” especially in older homes. The truth? It’s often a warning sign that something needs attention — and ignoring it can lead to expensive repairs or even safety issues. At Mike’s A/C LLC, we see this problem all the time. In this article, I’ll break down exactly what’s happening, the common causes, which ones are harmless versus dangerous, and what you should do next. Why Do Lights Dim When the AC Starts? When your air conditioner kicks on, the compressor (the heart of the system) needs a massive surge of electricity to start — often 3 to 5 times more power than it uses while running. This sudden high demand is called inrush current or startup surge. This surge pulls so much power that it temporarily lowers the voltage available to the rest of your home’s electrical system. Lights (especially incandescent and some LEDs) are very sensitive to voltage drops, so they dim or flicker until the compressor gets up to speed. A slight, brief dim (less than a second and only a small drop in brightness) can be normal. But if the lights dim dramatically, stay dim for several seconds, or this happens every single cycle, it’s time to investigate. Common Causes of AC-Related Light Dimming Here are the most frequent reasons we find in the field: Failing or Weak Start Capacitor The capacitor gives the compressor motor the extra “boost” it needs to start. When it weakens or fails, the compressor draws much more power from your home’s electrical system. This is one of the most common and fixable causes. Undersized or Aging Electrical Service Older homes with 100-amp or smaller panels may struggle with modern high-efficiency AC units. Long wire runs from the panel to the outdoor unit can also cause voltage drop. Loose Electrical Connections Loose wires, corroded terminals, or poor connections anywhere from the utility transformer to your breaker panel create extra resistance. When the AC surges, the voltage drop becomes very noticeable. Overloaded Circuits or Shared Wiring If lights and the AC share the same circuits or the panel is overloaded, the problem gets worse. Compressor Issues or Hard Starts A struggling compressor (due to low refrigerant, bad bearings, or other mechanical problems) can pull excessive amps on startup. Which Problems Can You Live With vs. Which Need Immediate Attention? Mild, brief dimming in a newer home with a properly sized electrical system → Often tolerable, but still worth checking. Dramatic dimming (lights go way down or flicker badly) → Red flag. This stresses your compressor and can lead to premature failure. Lights dimming + humming/buzzing from the AC unit → Likely a bad capacitor or compressor issue. Flickering that continues after the AC starts or happens with other appliances → Could indicate a bigger electrical problem (loose neutral, bad connections, etc.). Important Safety Note: Significant or frequent voltage drops can damage electronics, shorten the life of your AC compressor, and in rare cases point to fire hazards from loose connections. What Should You Do Next? Monitor it — Note how severe the dimming is and whether it’s getting worse. Have your AC serviced — A quick capacitor check and system inspection is usually inexpensive and can solve the problem fast. Call an electrician if the issue seems widespread in the house (not just when the AC runs). At Mike’s A/C LLC, we routinely handle these issues. Installing a hard start kit, replacing a failing capacitor, or recommending electrical upgrades can often eliminate the dimming and protect your system. Don’t Wait Until Summer Hits Hard Don’t let a small annoyance turn into a $1,000+ repair or a broken AC during the hottest days of the year. Early attention saves you money and keeps your home comfortable and safe. Questions about your lights dimming when the AC kicks on? Call or text me directly — I answer my own phone. 📞 (985) 516-3353 Mike’s A/C LLC Reliable AC Service You Can Trust
