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Why Is My Air Conditioner Leaking Water?

Air Conditioner Leaking Water

Water on the floor under an air-conditioning system can alarm any homeowner. The good news is that every drip points to a clear cause, and each cause has a direct repair. In most cases, you can solve the issue with basic tools, steady hands, and some patience.

In this guide, you will read the most common reasons for water leaks, see how each problem shows up, and learn the exact steps to stop the flow. Keep a rag handy, switch the unit off before you start, and follow each action in order. You will soon protect your home from damage and help your cooling system run at full strength.

1. Clogged Condensate Drain Line

Moist air passes over the cold evaporator coil. The coil pulls water from the air and sends it through the drain line. Dust, algae, and even small insects can block the narrow pipe. When the pipe blocks, the water backs up inside the air handler and spills over the edge. A slow drip turns into a steady leak that can stain ceilings or warp flooring.

Steps to Fix:

  1. Cut power at the breaker to stay safe.
  2. Find the PVC drain line next to the indoor unit.
  3. Remove the cap on the T-shaped vent if one is present.
  4. Push a stiff plastic tube or flexible brush through the pipe to loosen sludge.
  5. Attach a wet/dry vacuum hose at the outdoor end of the line.
  6. Seal the gap with a rag and run the vacuum for one minute.
  7. Pour a mix of warm water and white vinegar through the line to flush remaining debris.
  8. Replace the cap, restore power, and watch for new drips.

2. Damaged or Rusted Drain Pan

The drain pan sits under the evaporator coil and catches every drop that falls. Over time the metal pan can rust, or a plastic pan can crack. Small holes let water slip through before it reaches the pipe. The leak often shows up as a dark ring under the air handler.

Steps to Fix:

  1. Shut off power to the unit.
  2. Take off the service panel to reach the pan.
  3. Wipe the pan dry with a cloth to spot holes or cracks.
  4. If the damage is minor, apply epoxy putty rated for HVAC use.
  5. For large rust spots or cracks, buy a new pan made for your model.
  6. Slide out the old pan and fit the new one, keeping the drain hole aligned.
  7. Tighten mounting screws and reseal gasket edges with silicone.
  8. Reinstall the panel, switch the unit on, and confirm the pan remains dry.

3. Dirty Air Filter Restricting Airflow

A filter packed with dust blocks air from passing over the coil. The reduced airflow lowers coil temperature below freezing. Ice forms, melts, and floods the pan faster than it can drain. The leak often restarts each time the unit cycles.

Steps to Fix:

  1. Remove power to avoid moving parts.
  2. Pull out the filter from its slot.
  3. Hold the filter to light; replace it if light doesn’t pass through.
  4. Insert a new filter with the arrow pointing toward the blower.
  5. Vacuum dust from the filter slot and nearby returns.
  6. Let the unit sit off for one hour to thaw any ice on the coil.
  7. Turn the unit on and monitor moisture levels.
  8. Mark the calendar to change the filter every 30 days in summer.

4. Low Refrigerant Level Freezing the Coil

Refrigerant carries heat out of the home. When the level drops due to a leak, pressure inside the system falls. Low pressure makes the coil colder than normal. The coil then freezes and later dumps water into the pan as it thaws.

Steps to Fix:

  1. Turn off the unit to stop more ice from forming.
  2. Inspect copper lines for oily residue that signals a leak.
  3. Call a licensed HVAC technician to locate and repair the leak.
  4. Ask the technician to weigh in the precise charge listed on the nameplate.
  5. Request a system pressure test before the tech leaves.
  6. Once repaired, run the system and watch the sight glass (if present) for clear flow.
  7. Check the pan after two full cycles.
  8. Schedule annual checks to prevent future drops in charge.

5. Broken Condensate Pump

Basement or closet installations often rely on a small pump to lift water to a drain. If the pump motor burns out or the float switch fails, water collects until it spills.

Steps to Fix:

  1. Unplug the pump and pull the unit away from the wall.
  2. Press the float switch; if silent, the pump likely failed.
  3. Remove the top cover and clear any sludge that may jam the float.
  4. If the pump is dead, buy a replacement sized for your BTU rating.
  5. Disconnect tubing and power plug.
  6. Install the new pump and attach tubing.
  7. Pour water into the pump tank to ensure it starts.
  8. Restore the unit and verify no leaks persist.

6. Incorrect Thermostat Setting Raising Humidity

Setting the fan to “On” runs the blower even when the compressor rests. Moisture removed by the coil can blow back into the duct, form droplets, and return to the pan.

Steps to Fix:

  1. Change the fan setting from “On” to “Auto.”
  2. Lower the setpoint by two degrees.
  3. Use a hygrometer and aim for 45–50% relative humidity.
  4. Install a whole-house dehumidifier if needed.
  5. Clean vents and seal duct leaks with mastic tape.
  6. Review thermostat schedules to avoid fan-only runs.
  7. Recheck the pan after one day.

7. Unit Not Level After Installation

If the cabinet tilts even a few degrees, water pools on one side and spills over.

Steps to Fix:

  1. Place a bubble level on the cabinet.
  2. Check both axes.
  3. Loosen mounting bolts.
  4. Slide shims under the low side.
  5. Tighten bolts while steadying the unit.
  6. Seal gaps with foam.
  7. Confirm the drain line slopes downward.
  8. Monitor during the next cycle.

8. Faulty or Missing Insulation on Refrigerant Line

Without proper insulation, warm moist air condenses on the cold copper suction line.

Steps to Fix:

  1. Inspect the suction line for bare spots.
  2. Remove old insulation.
  3. Measure and cut closed-cell insulation.
  4. Slide over the pipe and tape seams.
  5. Use zip ties every three feet.
  6. Secure the line with hangers.
  7. Wipe condensate and monitor for new drips.

9. Blocked or Frozen Evaporator Coil Due to Dust

Dust blocks airflow over the coil, causing freezing and then leaks during thawing.

Steps to Fix:

  1. Cut power to the unit.
  2. Remove the access panel.
  3. Let ice melt naturally.
  4. Use a no-rinse coil cleaner.
  5. Restart after label-directed wait time.
  6. Replace the air filter.
  7. Clean return grilles.
  8. Schedule coil cleaning every spring.

10. Loose Drainage Connections

Threaded joints can loosen due to vibration, allowing leaks.

Steps to Fix:

  1. Turn off the unit.
  2. Wrap the joint with tissue to detect leaks.
  3. Hand-tighten the PVC nut.
  4. Use PTFE tape on threads if needed.
  5. Tighten with pliers gently.
  6. Run the unit and monitor.
  7. Replace damaged fittings.
  8. Check all drain path joints.

11. High Outdoor Humidity Causing Excess Condensation

On humid days, small splashes from the pan may overflow.

Steps to Fix:

  1. Close windows.
  2. Maintain a steady setpoint.
  3. Use a dehumidifier.
  4. Add attic insulation.
  5. Clear gutters.
  6. Seal weather-stripping.
  7. Upgrade to a variable-speed blower.
  8. Schedule seasonal maintenance.

12. Oversized AC Unit Short Cycling

Short cycles leave humidity behind, causing post-cycle drips.

Steps to Fix:

  1. Compare BTU rating using Manual J load.
  2. Replace with right-sized system if needed.
  3. Set fan to “On” for 10 minutes post-cycle.
  4. Install a smart thermostat.
  5. Add dampers for better airflow.
  6. Seal ducts in unused rooms.
  7. Keep interior doors open.
  8. Re-evaluate performance.

13. Malfunctioning Blower Fan

If the blower motor slows, airflow drops and the coil freezes.

Steps to Fix:

  1. Cut power.
  2. Open blower compartment.
  3. Spin fan wheel by hand.
  4. Check capacitor with multimeter.
  5. Clean wheel.
  6. Lubricate bearings (if allowed).
  7. Reinstall and restore power.
  8. Observe airflow.

14. Cracked or Clogged Secondary Drain Line

The backup drain line clogs or cracks, often leaking into ceilings.

Steps to Fix:

  1. Locate and inspect the line near the eave.
  2. Use vacuum to clear debris.
  3. Replace cracked parts with new PVC.
  4. Flush to confirm flow.
  5. Add a float switch for safety.
  6. Mark the line for visibility.
  7. Inspect monthly in summer.

15. Poor Attic or Crawl-Space Ventilation

Trapped air increases moisture, making the pan sweat.

Steps to Fix:

  1. Measure attic heat and humidity.
  2. Add ridge/soffit vents or powered fan.
  3. Cover air handler with insulation.
  4. Wrap ducts with R-8 insulation.
  5. Use a vapor barrier in crawl spaces.
  6. Confirm exhaust fans do not vent into attic.
  7. Reassess after upgrades.

Final Thoughts

Every water leak has a cause you can trace—whether it’s a clogged drain line, a rusty pan, or a frozen coil. Many fixes are safe for a careful homeowner with the right tools and patience. Yet some tasks—especially those involving refrigerant, motor repairs, or persistent drainage problems—demand advanced skills and diagnostic equipment.

When the issue is beyond a quick clean-up or part swap, protect your home and your cooling investment by calling trained professionals. Calfo Home Services has the expertise to identify the root of the leak, make precise repairs, and tune your system for long-term reliability. A prompt visit from their HVAC team will keep your floors dry, your air cool, and your mind at ease all summer.