A wet ceiling, water dripping out of a vent, or a puddle around the air handler is one of the most common AC service calls we run all summer. Texas humidity means our AC systems pull a tremendous amount of moisture out of the air every day — and when that moisture has nowhere to go, it ends up on your floor or in your drywall. Here is what causes it and what to do in the next ten minutes to stop the damage.
First — Stop the Damage
1. Turn the AC off at the thermostat. Set it to OFF, not just to a higher temperature. The system needs to stop pulling humidity out of the air to stop producing condensation.
2. Set the fan to OFF as well. Running the fan over a still-wet coil keeps moisture moving.
3. Put a bucket or tarp under the leak source if accessible. If the air handler is in the attic and water is dripping through the ceiling, a tarp on the attic floor and a bucket below the leak point limits drywall damage.
Once it is off and the bleeding has stopped, you can diagnose.
The 5 Causes — In Order of Most Common
### 1. Clogged Condensate Drain Line (60% of Calls)
What's happening: Your AC's evaporator coil pulls water vapor out of indoor air and condenses it into liquid water — about 5–20 gallons per day in Texas humidity. That water drains through a 3/4" PVC line that exits the house outside (or drains to a floor drain, condensate pump, or laundry standpipe).
Texas humidity plus warm, dark conditions in the drain line equals algae and biofilm growth. Over a season, the line gets restricted, then fully clogged. Water backs up, fills the drain pan, overflows, and drips through the ceiling.
How to tell this is your cause: Look at the air handler. Is there water in the drain pan (the metal or plastic tray under the unit)? If yes, the drain is clogged. Many modern systems have a safety float switch that shuts the AC off when the pan fills — if your AC "won't turn on" but you also see water in the pan, that is what happened.
The DIY fix (works most of the time): Find the access port on the drain line — usually a T-fitting near the air handler with a removable cap. Take the cap off. Use a wet/dry vacuum on the outdoor end of the drain line to suck the clog out. Run for 2–3 minutes. After clearing, pour a cup of distilled white vinegar (not bleach — bleach degrades PVC over time) into the access port to kill remaining algae.
If you cannot clear it yourself: A service call to clear a condensate line runs $150–$250. Worth it before water damage exceeds the cost.
### 2. Frozen Evaporator Coil
What's happening: When the coil freezes (dirty filter, low refrigerant, dirty coil, blocked vents), ice forms on the coil. When the system shuts off and the ice melts, the volume of meltwater overwhelms the drain pan — same effect as a clog.
How to tell: You had a recent issue where the AC was not cooling well, vents were blowing weak air, or you saw frost on the refrigerant lines. Now you have a leak.
The fix: Diagnose the freeze cause first — see our post on AC freezing up. If you have already replaced the filter and the coil refreezes, you have a refrigerant or coil-cleaning issue and need a tech.
### 3. Broken or Failed Condensate Pump
What's happening: If your air handler is below the level of where the drain water needs to go (basement units, some closet installations), there is a small pump that lifts the water up and out. When the pump fails, water collects until it overflows.
How to tell: Look for a small white plastic box near the air handler with a clear sight tube. If it is full of water and not pumping, the pump has failed.
The fix: Pump replacement is $250–$450. Same-day service.
### 4. Cracked or Rusted Drain Pan
What's happening: Older systems (10+ years) develop rust holes in the metal drain pan, or plastic pans crack. Water drains out the bottom of the pan instead of through the drain line.
How to tell: Drain line is clear, coil is not frozen, but water is still pooling under the unit. Visible rust or cracks on the pan.
The fix: Pan replacement is $200–$500 depending on access. On systems 12+ years old, often a sign that replacement is due.
### 5. Improperly Installed Unit (Pitch or Trap Issue)
What's happening: The drain line needs continuous downward pitch and a properly installed P-trap to drain. A bad install (line not pitched correctly, missing trap, kinked tubing) causes water to back up.
How to tell: The leak has been a persistent problem since the unit was installed, not something that developed gradually.
The fix: Re-pipe the drain line correctly. $200–$400 depending on length and access.
Why This Is Especially Common in Texas
Three reasons our service area sees this constantly:
1. Humidity. Central Texas summer humidity averages 65–80%. The AC pulls 10–20 gallons of water out of indoor air per day in peak summer — far more than systems in dry climates. Drain lines that work fine in Phoenix get overwhelmed in Pflugerville.
2. Long cooling seasons. Algae and biofilm need warm, dark, wet conditions. We give them all three for 8 months of the year. By the time July arrives, drain lines have been growing biofilm since March.
3. Attic-mounted air handlers. Most Central Texas homes built since the 1990s have the air handler in the attic. When the drain pan overflows, water has 8–14 feet to fall through ceiling joists and drywall — and you do not see it until it is dripping into the kitchen or staining the bedroom ceiling.
Prevention That Actually Works
Pour a cup of vinegar into the condensate drain access port every 60–90 days during cooling season. Single most effective preventive maintenance. Costs $3 in vinegar and 2 minutes of time. Prevents 80% of clogs.
Replace the filter every 30 days in summer. Reduces dust loading on the coil, which reduces gunk in the drain pan, which reduces clog rate.
Schedule annual AC tune-ups. A real tune-up includes flushing the drain line and inspecting the pan. We cover what's included in our HVAC tune-up cost guide.
Install a safety float switch if you do not have one. A float switch ($150–$250 installed) shuts the AC off when the pan fills up — preventing overflow. This is now code on new installs but many older systems do not have one.
When to Call
Call same-day if:
- Water is actively dripping through the ceiling
- The drain pan is full and you cannot access the line to clear it
- The coil is frozen and you have already replaced the filter
- You see rust or cracks on the drain pan
Schedule a non-emergency call if: the line is occasionally backing up and you want a thorough flush + safety switch installation before it becomes a flood.
Same-day AC leak service across Central Texas — Pflugerville, Bastrop, Taylor, Elgin, Georgetown, Hutto, Manor, Cameron, Rockdale, Brenham, and our full service area. Call (737) 260-7255. Texas license TACLB00027491E. Flat-rate pricing.