Why Your AC Is Leaking Water Inside

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Why Is My AC Leaking Water Inside the House (and How to Stop It)

If your AC is leaking water inside the house, don’t panic — it’s usually caused by a clogged drain line, dirty coil, or frozen evaporator. This guide explains what’s happening, how to stop the leak safely, and how to prevent future damage.

💧 Why Your AC Is Leaking Water Inside the House

  • Clogged condensate drain line: Algae, sludge, or debris block the PVC line so water backs up into the pan and overflows.
  • Dirty evaporator coil: Dirt restricts heat transfer, creating excess condensation that can overwhelm the drain pan.
  • Frozen evaporator coil: Low airflow or low refrigerant causes ice to form; when it melts, water spills over.
  • Cracked or rusted drain pan: Older pans can fail and leak even with a clear drain line.
  • Improper unit leveling: If the air handler isn’t slightly tilted toward the drain, water pools and spills.
  • Float switch failure: The safety switch designed to shut the system off doesn’t trip, allowing overflow.

🧰 Quick Fixes You Can Try (Safely)

  1. Power off the AC at the thermostat and breaker.
  2. Replace the air filter to restore airflow and reduce freezing risk.
  3. Clear the condensate line: Open the service port on the PVC drain line and pour about one cup of distilled vinegar. Wait 30 minutes, then flush with water. A wet/dry vacuum on the exterior drain outlet can help pull out clogs.
  4. Check the drain pan: Mop out standing water. Inspect for cracks or rust spots.
  5. Inspect coil for frost: If iced, keep system off and run “Fan Only” for 30–60 minutes to melt ice before restarting cooling.
  6. Confirm unit is level: The pan should slope gently toward the drain connection.
Tip: If you have a float switch, test it by gently lifting the float—your system should shut off. If it doesn’t, the switch may need replacement.

⚠️ When to Call a Professional

  • Water stains on ceilings or walls (possible hidden damage).
  • Repeated clogs even after vinegar flushes.
  • Frozen coil returns within hours or days—may indicate low refrigerant or airflow issues.
  • Electrical smells or water near wiring components.

🗓️ Prevent Future AC Leaks

  • Flush the condensate line with vinegar every 2–3 months.
  • Replace filters every 1–3 months to maintain airflow.
  • Schedule annual coil cleaning and system inspection.
  • Consider adding a secondary drain pan and a working float switch for overflow protection.
  • Keep the outdoor unit clean and clear to reduce system strain.

For additional homeowner HVAC tips, visit Energy.gov’s HVAC Maintenance Guide.

Last updated October 2025 — Reviewed by HVACMaintenanceGuide.com editorial team