Whether it’s light condensation or a bigger problem like a clogged drain or frozen coil, AC vent dripping water is a red flag worth investigating. Ignoring it can lead to ceiling stains, mold growth, or even costly structural damage.
This guide breaks down the most common causes, what you can safely fix yourself, and when it’s time to call in the pros.
Common Reasons Water Is Dripping from Your AC Vent
So, why is my AC vent dripping water? The answer often comes down to one of two things: excess moisture where it doesn’t belong, or a part of your HVAC system not doing its job.
Let’s look at the most frequent causes San Antonio homeowners face:
High Humidity and Poor Vent or Duct Insulation
Humidity is no stranger to South Texas. When your cold ductwork or vent grilles meet warm, moist air—especially in a poorly insulated attic—you get condensation. That condensation builds up on cold metal and drips right out of your vents.
This is known as “duct sweating,” and it’s especially common in older homes where ducts weren’t properly wrapped or sealed.
DIY Tip:
- Go into your attic and check the ductwork near the problem vent.
- If it feels wet or uninsulated, that’s your culprit.
- Add foil-faced duct insulation or fiberglass wrap around exposed ducts.
- Insulate the vent boot where it meets the ceiling.
Clogged Condensate Drain Line
Your AC doesn’t just cool the air—it also pulls moisture out of it. That moisture collects in a pan and exits through a drain line. But if that line gets clogged with algae, dust, or debris, water backs up.
Eventually, the water has nowhere to go but out—and that can mean leaking through your ceiling or dripping from your vents.
DIY Tip:
- Locate the PVC drain line near your indoor unit.
- Remove the cap and pour a cup of white vinegar to dissolve buildup.
- Alternatively, use a wet/dry vacuum on the outdoor drain line.
- Repeat every few months to prevent backups.
Frozen Evaporator Coil
A frozen coil is one of the most common and overlooked causes of water leaks.
Here’s what happens:
- Restricted airflow or low refrigerant causes the coil to freeze.
- When it thaws, the ice melts fast.
- That water can overwhelm the drain system and leak into ductwork or vents.
DIY Tip:
- Turn off your AC and let it thaw completely.
- Replace the air filter and ensure vents are open.
- If it freezes again, call a professional.
Rusted or Cracked Drain Pan
Over time, the pan under your evaporator coil can rust or crack—especially in older systems or those exposed to high humidity. When that happens, condensation doesn’t drain properly. It drips.
DIY Tip:
- Inspect the pan for rust or cracks.
- Seal small issues with waterproof epoxy.
- Long-term solution: Replace the pan with help from a professional.
Duct Leaks and Air Gaps Around Vents
Poorly sealed ducts or vents can leak cold air into a hot attic, causing condensation on metal vents. That moisture builds up and drips down.
DIY Tip:
- Feel around the vent grille for air leaks.
- Remove the grille and seal the edges with caulk or foam.
- Patch duct leaks with foil HVAC tape or mastic.
- Insulate exposed ducts to stop the sweating.
Failing Condensate Pump (If You Have One)
Some systems use a condensate pump to move water. If the pump fails or the float switch sticks, the pan can overflow—and leak through nearby vents.
DIY Tip:
- Pour water into the pump’s reservoir—does it turn on?
- Clean the float switch and reservoir.
- If the pump is dead, consider professional replacement.
Frozen or Short-Cycling AC Units
If your AC turns on and off too quickly, it may not remove enough humidity from the air. That lingering moisture causes condensation on ducts and vents.
Signs:
- Uneven cooling
- AC turns on/off every few minutes
- High humidity indoors
DIY Tip:
- Adjust the thermostat to prevent short cycling.
- Keep interior doors open to improve airflow.
External Leaks That Aren’t HVAC-Related
Sometimes, water near a vent is actually from a roof or plumbing leak.
How to tell:
- Leak appears during rain or even when AC is off
- Moisture near bathrooms or laundry rooms
- No signs of overflow at the AC unit
Solution:
Call a roofer or plumber to investigate if you suspect it’s not the HVAC.
DIY Troubleshooting Steps for AC Vent Leaks
Before you call a pro, try these homeowner-friendly checks:
- Turn off the system to stop further dripping.
- Check and replace your air filter.
- Inspect and flush the drain line with vinegar or a shop vac.
- Look for ice on the coil or refrigerant lines.
- Check for duct gaps or leaks in the attic.
- Test your condensate pump, if your system uses one.
If the dripping stops, great. If not—there may be a deeper issue.
When to Call a Professional HVAC Technician
Don’t wait if:
- Leaks persist after DIY fixes
- Coils continue to freeze
- The drain pan is rusted or cracked
- There’s visible mold, musty odors, or water damage
- Your condensate pump isn’t working
- You suspect a refrigerant leak
- You’re unsure what’s causing the problem
Comfort Tech’s technicians are trained to diagnose and repair these issues quickly—before they cause serious damage.
Preventative Maintenance Tips for San Antonio Homes
Humidity and heat are a constant here. Stay ahead of moisture issues with:
- Filter changes every 30–60 days
- Vinegar flushes for the drain line every 2–3 months
- Duct and vent insulation checks before summer
- Annual spring AC tune-ups
- Humidity control—consider a whole-home dehumidifier
A few small habits prevent a lot of expensive problems.
Protect Your Home from AC Water Damage
That slow drip isn’t just annoying—it’s a warning. Leaks from your AC vent can stain drywall, grow mold, and eventually wreck your ceiling.
With Comfort Tech, you don’t have to wait or guess. We’ll identify the issue, fix it right, and help you keep your cool.
Is Your AC Vent Leaking? Let’s Fix That.
Stop the drip before it turns into damage.
Schedule your AC service with Comfort Tech today and let our experienced San Antonio technicians find the issue, fix it fast, and help you stay cool—and dry.
Contact Comfort Tech Today
- Phone: (210) 920-4645
- Email: service@comforttechsac.com
- Website: www.comforttechsac.com
- Serving: San Antonio & nearby communities
