AC Condensate Leak in the Attic? What to Check

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Here's something a lot of North Texas homeowners don't realize: your air conditioner makes water. A lot of it. As warm, humid air passes over the cold coil, moisture condenses and drips into a pan, then drains out through a condensate line. In a long Texas summer, with the AC running nonstop, that's a steady stream.

In many homes around here, the AC air handler sits in the attic. When that water can't drain, it ends up in your insulation and your ceiling. Here's how the system works and how to keep it from becoming a water loss.

How Does AC Condensate Drainage Work?

The basic parts:

• Evaporator coil: the cold part inside the air handler where moisture condenses
• Primary drain pan: directly under the coil, catching water
• Condensate line: usually PVC pipe that carries water outside or to a drain
• Secondary or emergency drain pan: a larger pan under the whole unit, a backup if the primary fails
• Secondary drain line: often drains to a visible spot, like over a window, so you notice when it's running
• Float switch: a safety switch that can shut off the AC if water rises in the pan

Why Do AC Drains Fail?

• Clogs. Algae, sludge, dust and debris build up in the line over time. This is the big one.
• Disconnected or cracked lines. Attics get hot, and fittings can shift or crack.
• Rusted pans. Older metal pans can rust through.
• Missing or failed float switch. Without it, the pan can overflow silently.
• Poor slope. Lines need a downhill slope to drain.
• Frozen coils. A dirty filter or low refrigerant can freeze the coil, and when it thaws, it can overwhelm the pan.

What Are the Warning Signs?

• Water dripping from the secondary drain outside, often over a window. That's your system telling you the primary drain is clogged.
• A ceiling stain near the air handler or below the attic access
• Water in the emergency pan when you peek in the attic
• The AC shutting off unexpectedly, which can mean the float switch tripped
• A musty smell near vents or the return
• Water around an indoor unit in a closet

What Can I Do to Prevent an Overflow?

1. Change your air filter regularly. A clogged filter can freeze the coil.
2. Know where your condensate line exits outside and check that it's dripping when the AC runs.
3. Look at the secondary drain. If it's dripping, call your HVAC tech.
4. Peek in the attic a couple of times each summer, with a flashlight, safely. Look at the pan.
5. Ask your HVAC tech about a float switch if you don't have one.
6. Schedule regular HVAC maintenance, including drain line cleaning.

Some homeowners flush the line with a little vinegar through the access port. Follow your HVAC technician's guidance for your system.

What Should I Do If the Ceiling Is Wet?

• Turn off the AC at the thermostat to stop the water
• Put a bucket under any drips
• Stay out from under a sagging ceiling
• Take photos
• Call an HVAC tech to clear the drain and check the system
• Call for a moisture assessment of the ceiling and insulation

Attic water spreads through insulation and along joists. Wet insulation holds water against the drywall and rarely dries well. Read wet drywall: dry or replace for how we decide.

Can a Small AC Leak Lead to Mold?

Yes. A slow, repeated leak keeps insulation and drywall damp in a hot attic, which is ideal for mold. If you've had repeated drips, have it checked.

Who Do I Call?

An HVAC company fixes the AC and drain. CMDR Restoration, our mitigation partner (licensed by TDLR, RCO #1801), dries the attic and ceiling. G3 rebuilds the drywall, texture and paint. Learn more on our water damage page or call (945) 300-9018. Learn how to prevent mold after water damage from a wet ceiling.

Frequently Asked Questions

Keep learning: see our Water Damage page, read Appliance Leaks: Washer, Dishwasher, Water Heater, or read what homeowners say in our customer reviews.