Lennox High Inrush Current / Voltage Sag

Lennox air conditioner causes lights to dim or flicker in the home when the compressor starts.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Compressor drawing high locked-rotor amps, Weak utility service or undersized wiring, Failing run capacitor, Shared electrical circuit with lighting

How to Fix / Troubleshooting

Safety: Electrical issues can be hazardous. Consult an electrician or HVAC technician if unsure.

  • 1. Verify dedicated circuit: Ensure the Lennox condenser is on its own breaker and not sharing with lighting circuits.
  • 2. Check and replace capacitor: A weak run capacitor can increase starting current. Replace with the correct Lennox-rated capacitor if out of spec.
  • 3. Consider hard-start kit: A technician can install a Lennox-approved hard-start kit to reduce inrush current.
  • 4. Have service entrance evaluated: If dimming is severe, an electrician should check the main service capacity and connections.

Note: Mild, brief dimming is common, but significant or worsening flicker should be investigated.

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Repair Difficulty

Medium 3/5

Required Part

Lennox Dual Run Capacitor
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