Why Do Lights Flicker When the AC Turns On? (And How to Fix It)

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Is Your Home’s Electrical System at Risk?

If your lights flicker when the AC comes on, you’re not alone—this common issue can signal anything from a minor annoyance to a serious electrical problem. While a slight dimming is normal, frequent or severe flickering may indicate wiring issues, overloaded circuits, or a failing HVAC system. In this guide, we’ll explore the causes, risks, and solutions to keep your home safe and well-lit.

Common Causes of Light Flickering When AC Starts

  1. Voltage Drop from High Inrush Current
    • Air conditioners draw a surge of power when starting (known as inrush current), which can temporarily reduce voltage to other circuits. A brief flicker is normal, but persistent flickering suggests an underlying issue (source: Energy.gov).
  2. Overloaded Circuit
    • If your AC and lights share a circuit, the combined load may exceed capacity. Older homes with 15-amp circuits are especially prone to this.
  3. Loose Wiring or Faulty Connections
    • Worn-out breakers, loose neutral wires, or corroded electrical panels can worsen flickering. This poses a fire hazard and requires immediate attention (source: NFPA).
  4. Undersized Electrical Service
    • Homes with 100-amp panels or outdated wiring may struggle to handle modern AC units. Upgrading to a 200-amp panel can resolve this.
  5. Failing AC Compressor or Capacitor
    • A struggling compressor draws erratic power, causing lights to dim or flicker. HVAC maintenance can prevent further damage.

How to Diagnose and Fix the Problem

Step 1: Check for Simple Issues First

  • Test Different Lights – If only one light flickers, the bulb or fixture may be faulty.
  • Plug AC into a Dedicated Circuit – Avoid sharing circuits with high-wattage appliances.

Step 2: Inspect Your Electrical Panel

  • Look for tripped breakers, buzzing sounds, or burnt smells.
  • Hire an electrician to test voltage drop during AC startup (should be less than 5%).

Step 3: Evaluate Your AC System

  • Dirty filters or refrigerant leaks force the AC to work harder, increasing power surges. Schedule HVAC maintenance to rule out mechanical issues (source: ENERGY STAR).

Step 4: Upgrade Your Wiring or Panel

  • For older homes, a panel upgrade or a dedicated 240V circuit for the AC may be necessary.

When to Call an Electrician

Seek professional help if you notice:

  • Frequent, severe flickering in multiple rooms.
  • Burning odors or scorch marks near outlets.
  • Circuit breakers that trip repeatedly.

Preventative Measures

  • Install LED bulbs (less sensitive to voltage fluctuations).
  • Use a hard-start kit for your AC to reduce inrush current.
  • Consider a whole-house surge protector to stabilize voltage.

While minor flickering is typical, persistent issues could endanger your home. Addressing loose wiring, upgrading electrical capacity, and maintaining your AC system will ensure safe, stable lighting. For severe cases, consult a licensed electrician—find certified pros via Angi or HomeAdvisor.

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