puddle of water leaking from underneath air conditioner unit inside house
puddle of water leaking from underneath air conditioner unit inside house

“Why is my air conditioner leaking water?” is a simple question with a not-so-simple answer. Air conditioners produce condensation, or water, as part of their normal functioning. When the air conditioner absorbs heat and humidity from inside the house, moisture condenses on the evaporator coils in the indoor air conditioning unit. The condensation drips off and collects in the drain pan, which emDrops of water flowing out of the air conditioning ductpties into a PVC pipe called the condensate drain line. The drain line carries the water from the indoor unit and opens outside near the condenser.

If the condensation cannot evaporate or be carried away from the unit, the unit may leak water inside the house. The first step is to determine why the water is not draining or evaporating as it should. If you can diagnose the problem, you can take steps to resolve it.

Common Reasons for Air Conditioner Leaking Water

If your air conditioner is leaking water, the issue could be any of the components that deal with the condensation it produces, such as the condensate drain line, the evaporator coils, the drain pan, or the condensate pump.

clogged central air conditioner condensate drain line illustration

Clogged Condensate Drain Line

The drain line carries the water away from the indoor unit and empties outside near the condenser. The drain line is subjected to the outside elements and remains moist, so it can quickly become clogged with algae, sludge, dirt, debris, and even bugs. If the drain line contains a clog, water accumulating in the drip pan has nowhere to go, the pan overflows, and water pools beneath the unit.

How to unclog a condensate drain line

  1. Turn off the air conditioner at the thermostat and the circuit breaker panel.
  2. Locate the drain line outside near the condenser. It is a PVC pipe with a plastic cap.
  3. Remove the cap and look for the clog. A flashlight may be helpful.
  4. Remove the clog, but avoid pushing it further in the pipe. If the clog is unreachable or the drain line has never been cleaned, move on to Step 7.
  5. Slowly pour 1 cup of distilled white vinegar into the pipe.
  6. Replace the cap and wait 30 minutes before turning the air conditioner on.
  7. If you cannot get to the clog or the drain line has never been cleaned, use a wet/dry vacuum to suck up the clog and the trapped water. Let the vacuum run for 3-4 minutes. Replace the cap.

Dirty Evaporator Coils

An air conditioner cools your home by removing the heat and humidity from the air via refrigerant flowing through the evaporator coils. The cold refrigerant causes moisture to condense on the coils. If the evaporator coils are dirty, warm air cannot circulate near the coils causing the coils to become too cold. Instead of evaporating, the condensation turns to ice on the coils. When the air conditioner shuts off, the ice melts, and the excess water pools beneath the unit.

How to clean your evaporator coils

One way to clean evaporator coils is with a no-rinse evaporator coil cleaner.

  1. Turn off the air conditioner at the thermostat and the circuit breaker panel.
  2. Remove the access panel and locate the evaporator coils.
  3. Remove dust from the coils with compressed air or a dog brush.
  4. Apply a no-rinse evaporator coil cleaner following the instructions on the can. Re-apply the cleaner to any areas that remain dirty.
  5. Replace the panel and turn the power supply back on.

Alternatively, you can clean the coils with soap, water, and vinegar. The coils must be removed first.

  1. Turn off the air conditioner at the thermostat and the circuit breaker panel.
  2. Remove the access panel and locate the evaporator coils. Remove the coils from the unit.
  3. Combine water and a few drops of dish detergent in a spray bottle. Spray the mixture onto the coils, and let them sit for several minutes. Use a brush to clean the dirt from the coils.
  4. Combine a 1:1 ratio of water and distilled white vinegar in another spray bottle. Spray the coils to remove leftover grime and disinfect them.
  5. Rinse the coils with water and allow them to air dry for several hours.
  6. Replace the coils and the access panel. Turn the power supply back on.
disconnected air conditioner drain line

Disconnect Drain Line

A disconnected or improperly installed drain line will leak water. Condensation in the air conditioner’s drip pan drains into a PVC pipe called the condensate line or drain line. The drain line carries the water away from the indoor unit and empties outside. Locate the drain line near the indoor unit and check if the connection is secure.

How to fix disconnected drain line

  1. Turn off the air conditioner at the thermostat and the circuit breaker panel.
  2. Use a screwdriver or pliers to reconnect the drain line. Straighten any kinks in the line.
  3. Turn the power supply back on and check for leaking water.

Damaged Drain Pan

Moisture condenses on the evaporator coils, drips off, and collects in the drain pan. Air conditioners typically have two drain pans, the primary drain pan beneath the evaporator coils or the air handler and the secondary or backup drain pan at the bottom of the unit. The drain pan empties into the drain line, which carries the water away from the house. If the drain pan is cracked or corroded, the water may drip and pool underneath the unit.

You can quickly inspect the drain pan for leaks. Turn off the air conditioner at the thermostat and breaker panel. Remove the access panel and locate the drip pan. Slowly pour a gallon of water into the pan. Use a flashlight to observe the water’s flow. Water will drip from a small crack and flow from a large gap. The water will flow into the drain line if the pan is not damaged.

rusted corroded central air conditioner drain pan

How to fix a damaged drain pan

It’s best to replace a damaged drain pan. However, minor cracks can be repaired with waterproof sealant.

  1. Turn off the air conditioner at the thermostat and the circuit breaker panel.
  2. Remove the access panel and locate the drain pans. The primary drain pan is beneath the evaporator coils or the air handler and the secondary or backup drain pan is at the bottom of the unit.
  3. The primary pan is usually welded on. If this pan is cracked, you must dry its contents with a wet/dry vacuum or a rag while it’s attached to the unit. The secondary pan can be removed and emptied of its contents.
  4. Sand the area around the crack with fine-grit sandpaper to help the sealant adhere.

Apply the sealant to the crack. Let it cure for 2 hours—sand down the excess sealant.

  1. Test the repair by slowly pouring in a gallon of water and visually inspecting it for dripping water. Alternatively, run the air conditioner for a few hours before visually checking the pan for drips.

Broken Condensate Pump

Some air conditioners use a condensate pump instead of gravity to push water from the condensate drain pan into the drain line. A broken pump will cause the drain pan to fill with water and spill over. An overflowing drain pan does not necessarily indicate a broken pump. Other issues, such as a clog, can also cause water to spill over.

How to fix a damaged condensate pump

  1. Turn off the air conditioner at the thermostat and the circuit breaker panel.
  2. Remove the access panel and locate the drain pan. The primary drain pan is located beneath the evaporator coils or the air handler and is usually welded on. Dry up its contents with a wet/dry vacuum or a rag, and inspect the pan for debris blocking the intake hose. Make sure nothing is stuck between the pump parts or connections with other pipes. Check for loose wires.
  3. If the pump is broken, replace the pump.
central air conditioner unit condensate pump

Can dirty filter cause air conditioner to leak water

Can a dirty filter cause an air conditioner to leak water? Yes, a dirty air filter can cause an air conditioner to leak water, even though it does not directly deal with the condensation the unit produces. A dirty filter causes leaks by impeding airflow around the evaporator coils.

An air conditioner cools your home by removing the heat and humidity from the air via refrigerant flowing through the evaporator coils. The cold refrigerant causes moisture to condense on the coils. If the air filter is dirty, warm air cannot circulate near the coils causing the coils to become too cold. Ice forms on the coils and can form on the filter, too. When the air conditioner shuts off, the ice melts, and the excess water pools beneath the unit.

If the air filter appears dirty, wet, or has not been changed in the last three months, replace it with a new one. Regularly changing the air filter is essential to maintaining your air conditioner. Air filters should be changed every 30-90 days, depending on the quality of the filter.

Is a Leaking Air Conditioner Dangerous?

Is water leaking from the air conditioner dangerous? It is likely not harmful. Most of the time, leaking water results from a blockage or dirt accumulation in the air conditioner unit. While this isn’t dangerous, it could cause damage to your home and be an expensive repair if left unresolved.

If the fluid leaking from your A/C unit is refrigerant, it’s cause for concern. Refrigerant leaks aren’t as common as water leaks, but they are much more hazardous. Refrigerant is potentially lethal if it evaporates to become a gas. If your air conditioner is leaking refrigerant, get it repaired right away.

Some signs that your air conditioning system is leaking refrigerant:

  • Your electrical bill is higher than usual
  • The house doesn’t cool down as quickly as usual
  • The air conditioner is blowing warm air
  • Ice has built upon the A/C unit

Conclusion

All air conditioners produce water in the form of condensation. If your air conditioner is leaking water inside the house, there likely is an issue with the component that produces the condensation, one of the components that carry the condensation away, or the air filter.

A homeowner may locate the problem by inspecting the condensate drain line, the evaporator coils, the drain pan, the condensate pump, and the air filter. In many cases, the homeowner can take steps to resolve the problem. If it continues to leak water or if you are uncomfortable with servicing your air conditioner, an HVAC professional can help.

Air conditioning

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