Your AC pulls moisture from the air as part of its cooling job; seeing some occasional condensation drip outside isn’t concerning. Finding water leaking inside your home, however, points to bigger issues, such as blocked drain lines or cracked drip pans.
Taking simple measures such as regular inspections and timely filter replacements helps in preventing AC leaks.
In this article, I will share insights from HVAC pros to help you understand why your AC leaks happen and tips on what to do next.
Understanding Normal AC Water Production
Your air conditioner naturally pulls moisture out of warm indoor air, making your home feel less humid. When the humid air hits the cool evaporator coil, condensation forms—just like droplets appearing on a chilled glass in summer.
That condensation collects into a drain pan beneath your unit and flows outside through a condensate drain line.
Gary Bregani from Willowbrook Plumbing & Heating explains: “If it’s pooling outside near the drain line, that’s normal. If the inside air feels damp and musty, or you notice water near the vents, it’s time to investigate.”
Good to Know: A typical home AC can pull between 5 and 20 gallons of moisture a day in humid weather. Meteorologist Alan Sealls showed one air conditioner unit extracting over three gallons in just five hours, highlighting how hard your AC works when humidity spikes.
Common Causes of AC Water Leaks
1. Clogged Drain Line
| DIY or Professional: DIY Difficulty Level: Easy to Medium Time Required: 30 to 60 minutes Tools Needed: Wet/dry vacuum, rubber gloves, white vinegar, clean water, rag |
Your AC’s drain line allows condensation to safely exit your home. However, Bregani says the most frequent issue he finds with AC leaks traces back to plugged-up drain lines.
Usually, dirt, debris buildup, or even algae growth blocks this pipe and keeps water from flowing away properly. This leads to backups, puddles appearing under your indoor unit, or unusual damp spots on ceilings or walls if your AC is in the attic.
How to identify it: A clear warning sign shows up if the outdoor pipe doesn’t drip during operation; this likely indicates you’ve got a clog brewing.
What to do:
- Turn off your thermostat and switch off the AC breaker to avoid any electrical hazards.
- Find the PVC condensate drain line near the evaporator coil inside or on an exterior wall, then remove the service port cap.
- With rubber gloves on, peek into the port and pull out any dirt or sludge you can reach by hand.
- Seal a wet or dry vacuum hose over the port opening with a rag and run it for 1 to 2 minutes to suck out hidden gunk.
- Pour 1 cup of white vinegar into the drain line, let it sit for 30 minutes to kill algae, then flush with clean water until it runs clear.
- Replace the port cap, restore AC power, and run the system. Watch the outdoor drain tube for a steady drip to confirm the line is clear.
My Tip: Every time you change your air filter (about 1 to 3 months), give the line a quick vinegar flush to keep it flowing freely.
2. Damaged Drain Pan
| DIY or Professional: DIY (minor repairs) or Professional (major damage) Difficulty Level: Medium Time Required: 1 to 2 hours (repair) or 2 to 4 hours (replacement) Tools Needed: Flashlight, towels, HVAC sealant/waterproof tape, replacement pan (if needed) Estimated Cost: $10 to 30 (repair supplies) / $30 to 150 (replacement pan) |
An AC drain pan catches the water dripping from your unit’s evaporator coil, guiding it into the drain line. Bregani points out that these pans become a weak spot—over time, they easily crack or rust, particularly in older air conditioners.
If deterioration sets in, water has no safe path out of the unit and drips onto floors or ceilings.
How to identify it: Switch OFF your thermostat and AC breaker before opening the front panel of your indoor unit (air handler). With a flashlight, inspect beneath the evaporator coil for standing water, rust-colored stains, or visible cracks in the pan—those are clear warning signs.
Here’s what to do next:
- First, dry any standing water completely using towels.
- Pour a small amount of clean water into the pan to find exactly where the leaks appear.
- Thoroughly dry again before covering small holes or minor cracks with HVAC-safe sealant or heavy-duty waterproof tape over the leak. Allow 24 to 48 hours drying as directed on the packaging.
- Turn the breaker back on and run the AC for a few minutes. Check under the unit and outside for steady water flow—no leaks.
*Recommendation: If cracks are big or rust is severe, buy a replacement pan at a hardware store (about $30 to $150). Disconnect the PVC drain line, unclip the old pan, slide in the new one, and reconnect the drain tube with PVC cement.
Warning: Hire an HVAC technician if your repairs involve touching refrigerant lines, removing the evaporator coil, or reaching tricky areas you can’t easily fix yourself. These tasks require expertise and aren’t safe DIY projects.
3. Frozen Evaporator Coils
| DIY or Professional: DIY (basic thawing) or Professional (refrigerant issues) Difficulty Level: Easy to Professional Time Required: 3 to 24 hours |
Evaporator coils usually freeze when dirty air filters or poor airflow interfere with the coil’s heat transfer. Without sufficient hot air passing over them, the coils become too cold, and ice starts forming. Then, it melts, leaving you with spilled water outside of your drain pan.
How to identify it: You might spot an icy buildup around indoor components or notice noticeably weaker cooling output than usual, along with unexpected leaks near your AC unit. For more detailed information about why freezing occurs, check out our article ‘What Causes an AC to Freeze Up?’
What to do:
- Immediately switch off your thermostat and allow the ice to melt fully.
- Inspect and replace the air filter immediately if it’s dirty; that’s typically step one for restored airflow.
- Allow ice plenty of time to melt before switching it back on—see our step-by-step guide in ‘How to Unfreeze Your AC Unit’.
If the problem returns, call an HVAC pro to check refrigerant levels and coil health.
4. Dirty Air Filter
| DIY or Professional: DIY Difficulty Level: Easy Time Required: 5 to 15 minutes (disposable filter) or 15 to 30 minutes cleaning, 12 to 24 hours drying (washable filter) Estimated Cost: $10 to 30 (filter cost) |
Whenever you neglect your air filter for too long, it clogs with dust and grime, causing poor airflow across the evaporator coils.
Bregani warns: “The first thing I tell customers is to check their air filters. If it’s dirty, airflow gets blocked and coils freeze up.”
How to identify it: Inspect your filter monthly. If it looks grey with dust and debris, you need a new one, or clean it if you have a washable filter.
What to do: Change standard HVAC filters every 30 to 90 days. High-efficiency pleated filters may last longer, but still check them monthly in humid months. A clean filter helps air flow freely and prevents coil freeze-ups. For detailed steps, check our guide on How to Clean Your AC Filter.
5. Low Refrigerant Levels
| DIY or Professional: Professional Only Time Required: 1 to 3 hours Estimated Cost: $210 to $1,200 (professional service) |
Refrigerant absorbs indoor heat to cool down your home’s air. When your AC is low on refrigerant (often due to leaks), there’s insufficient pressure, and the evaporator coils drop in temperature.
If that happens, ice starts building up—once it melts, you’re left with puddling, water inside or around the unit.
How to identify it: Bregani mentions that sometimes you’ll notice odd noises from your AC, such as hissing or bubbling sounds, before spotting actual leaks. Other signals include weak airflow, inadequate cooling, and wet patches appearing beneath your AC or furnace.
What to do: This isn’t safe for DIY repairs. Call an HVAC technician who will accurately diagnose any leaks present, carefully seal them, and recharge your refrigerant levels.
6. Improper Installation or Leveling
| DIY or Professional: Professional Only Time Required: 1 to 4 hours Estimated Cost: $150 to 500 (professional service) |
Your indoor AC unit needs to sit level so that condensation flows directly into the drain line. If installers tilt your equipment incorrectly, water accumulates inside the drip pan and may overflow onto floors or ceilings.
How to identify it: Check beneath the evaporator coil near your indoor air handler. Standing water noticeably pooling to one side or beneath the unit housing often indicates improper leveling.
What to do: Have an HVAC professional adjust the mounting brackets or position shims under your air handler until it’s fully level. They’ll also make sure drain lines stay secured firmly without sagging spots where water can become trapped.
Signs Your AC Leak is Serious
Most AC leaks start small, but ignoring them can quickly lead to costly HVAC repairs and lasting home damage. As HVAC expert John Gabrielli from Air Temp Solutions highlights:
“If you detect mildew odors, gurgling sounds by the unit, or increased indoor humidity, a leak is probably brewing. These are most often noticed before you can see water. Begin with a visual inspection.”
Here’s how you know it’s time to act fast:
- Steady water is pooling under your indoor unit or dripping onto ceilings.
- Damp walls or moldy smells around vents and return air areas.
- Noticeable drop in cooling performance paired with higher power bills.
- Unexpected gurgling or hissing noises (could be refrigerant problems)
Regular inspections keep things running smoothly; however, always bring in an HVAC professional immediately if these symptoms become obvious around your home cooling system.
FAQ About AC Leaking Water
You should shut off the air conditioner immediately when you see water leaking. Experts warn to turn off the indoor unit and pull the outside disconnect because running it can push more water into your house.
Moreover, if the water reaches wiring or controls, it may short out components or even cause a fire risk.
You really shouldn’t wait more than a day or two to have the leak checked. Water damage and mold can start quickly, so the longer the unit runs or sits wet, the higher the repair bill becomes.
HVAC pros say simple fixes, such as clearing a drain, usually take less than an hour, while bigger repairs rarely exceed a few hours
How to Prevent Your AC from Leaking Water
Your air conditioner naturally extracts moisture every time it runs, but it’s your job to make sure this water safely flows outside instead of into your living room.
Simple maintenance routines like checking drain lines for clogs, changing filters every month, and regularly inspecting drip pans can save your wallet from expensive future issues.
An overlooked leak can result in extensive water damage that’ll require expensive repairs or even spending thousands on new AC installation.
As Gabrielli advises: “You will be able to distinguish between ordinary condensation and a leak by looking for standing water near the bottom of the unit or on surrounding walls. A little water is okay. Standing water is not.”
Read More:
- How Much Does an HVAC Inspection Cost?
- How Much Does HVAC Maintenance Cost?
- How to Quiet a Noisy Air Conditioner
Main Image: Water leaking from AC unit. vach / Adobe Stock
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