Finding a puddle under your indoor AC unit — or a water stain spreading across the ceiling below it — is one of those problems that quietly gets expensive. Your air conditioner naturally pulls moisture out of the air, and that water is supposed to drain safely away. When it ends up on your floor instead, something in the drainage path has failed. The good news: the causes are a short list, and your first move can stop the damage in minutes.
Do this first
Turn the system off at the thermostat. That stops the unit from producing more condensate while you find the source. Then soak up any standing water and move anything valuable out from under the unit or the ceiling below it. Water and an energized air handler don’t mix, and a slow drip can ruin drywall, insulation, and flooring long before you notice a stain.
Quick diagnosis by symptom
Match what you’re seeing to the most likely cause:
| What you notice | Most likely cause | What to do |
|---|---|---|
| Steady drip or overflow from the indoor unit, no ice | Clogged condensate drain line | Turn off; clear the drain line, or call a tech |
| Water pooling directly under the air handler | Rusted or cracked drain pan | Turn off; the pan needs replacement |
| Ice on the copper lines or coil, then water when it melts | Frozen evaporator coil thawing | Turn off, let it thaw fully, then inspect |
| Weak airflow and a very dirty filter, plus leaking | Dirty filter starved the coil and froze it | Turn off, replace the filter, let it thaw |
| Water near the unit but the pan is dry | Disconnected or slipped drain line | Turn off; reconnect/reseat the drain line |
| Leak plus a musty smell | Standing water and biofilm in the drain | Clear and treat the drain; check the pan |
A clogged condensate drain line
This is the single most common cause of an indoor AC leak. The condensate drain is a small pipe that carries away the water your coil pulls from the air. Over time it clogs with algae, dust, and — in El Paso — hard-water scale, all of which thrive in that damp line. When it’s blocked, water backs up and overflows the drain pan onto your floor or ceiling. Our dry, dusty air and hard water make this happen faster here than in most climates. A wet/dry vacuum on the outdoor end of the line can sometimes pull the clog free; a persistent or repeat clog is worth a professional cleaning, which is a routine part of AC repair and service.
A rusted or cracked drain pan
Underneath the evaporator coil sits a pan that catches condensate and routes it to the drain. After years of standing water, that pan can rust through or crack, and then water drips straight down regardless of whether the drain line is clear. A damaged pan can’t be patched reliably — it needs to be replaced by a technician who can access the coil.
A frozen evaporator coil that’s thawing
If you see ice on the copper lines or the indoor coil, the “leak” is that ice melting. A coil freezes when airflow is too low (usually a dirty filter) or refrigerant is low from a leak. Once the system cycles off, all that ice melts at once — far more water than the pan and drain can handle, so it spills inside. Turn the system off and let it thaw completely before running it again, and address the root cause: change the filter, and if the coil freezes again, have the refrigerant charge checked.
A dirty air filter
A clogged filter is the quiet root cause behind many leaks. It restricts airflow across the coil, the coil drops below freezing, ice forms, and then it melts and overflows. The U.S. Department of Energy recommends inspecting filters monthly during heavy-use months and replacing them when dirty — in dusty El Paso, often every 30–60 days. It’s the cheapest, easiest step and it prevents both leaks and weak cooling. Keeping the drain and coil clean also protects your indoor air quality, since a damp, clogged drain pan is where mold and musty odors start.
A disconnected or slipped drain line
Sometimes the pan is fine and the line is clear, but a fitting has come loose or the drain line has slipped off, so condensate drips before it ever reaches the drain. This is a straightforward reconnection for a technician, and worth checking after any recent work near the air handler.
When to call
Call if the leak comes back after you’ve cleared the filter and drain, if you see a cracked or rusted pan, if the coil keeps freezing, or if water has already reached your ceiling or walls. Repeated leaks point to a drainage or refrigerant issue that won’t fix itself, and catching it early keeps a cheap repair from becoming water damage.
How to prevent it
Nearly every indoor leak traces back to a skipped filter change or a drain line that never gets cleaned. A yearly maintenance visit before summer clears the condensate line, checks the pan, and verifies airflow and refrigerant — the three things that cause leaks — so you’re not mopping up on a 105° afternoon.
When the water keeps coming, or you see ice on the coil, shut the system off and call. We offer same-day service Monday through Friday, and a free quote on any repair or replacement.