AC Leaking Water? Here's What Was Really Wrong

A step-by-step look at a real AC leak repair, from water pooling near the indoor unit to the fix

A clogged drain and a frozen coil aren’t always separate problems, sometimes one causes the other. Here is the exact diagnostic process our certified technicians used to trace this leak back to where it actually started.

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Case Snapshot

Symptom

Water pooling near the indoor unit

System

Central Air Conditioning

Location

Harwood Heights, IL

Diagnosis

Clogged drain + frozen coil from a dirty filter

Time to Repair

Same visit, under 1.5 hours

Outcome

No more leaking, proper drainage restored

The Problem

A Harwood Heights homeowner called Dara Appliance Repair after noticing water pooling on the floor near the indoor air handler in her basement. It didn't seem to leak right when the AC started up, it showed up more after the system had been running for a while, which made it hard to catch in the moment.

She wiped it up each time and hoped it would resolve on its own, but the puddle kept coming back on hot days.

The Diagnostic Process

Checked the condensate drain line first

Our technician found significant algae and sludge buildup inside the primary drain line, a common and straightforward cause of AC leaks. The line was cleared and flushed.

Retested and found the leak returned

Drainage improved with the line cleared, but the leak came back on the next run cycle, meaning the clog wasn't the whole story.

Inspected the evaporator coil directly

The coil had a visible buildup of ice on it. As that ice melted during and after each cycle, it was producing more water than the drain and pan could handle right away, which explained the delayed leak pattern.

Investigated why the coil had frozen

The air filter was significantly dirty and clogged, restricting airflow across the coil enough to let it run too cold and ice over, a well-known chain reaction from a simple maintenance issue.

Confirmed refrigerant levels were normal

Low refrigerant is another common cause of coil freezing, so the technician checked pressures directly and confirmed the charge was correct, isolating the restricted airflow as the actual trigger.

The Root Cause

A dirty air filter had restricted airflow enough to freeze the evaporator coil, and the meltwater from that ice was more than the already partially clogged condensate drain could keep up with. The two issues made each other worse: clearing the drain alone helped, but the coil kept freezing and overproducing water until the airflow problem was fixed too.

The Fix

With both causes confirmed, our technician completed the repair in a single visit:

Thoroughly cleared and flushed the condensate drain line
Replaced the dirty air filter to restore proper airflow across the coil
Let the frozen coil fully thaw before resuming operation, rather than restarting the system right away
Ran the system through a complete cooling cycle to confirm proper drainage with no leaking and no further icing

The Result

The system now drains properly through a full cooling cycle with no water pooling near the indoor unit, and the coil no longer ices over now that airflow is restored. The $89 diagnostic fee was waived since the customer moved forward with the repair, and the repair is backed by our standard 3-month warranty. As a first-time customer, she also received 10% off the total repair cost.

Common Causes of an AC Leaking Water

Cause	Signs	DIY-Fixable?
Clogged condensate drain line	Water pools near the indoor unit, may trigger a safety switch to shut the system off	Sometimes, a wet/dry vac at the outdoor drain termination can help
Frozen evaporator coil	Leak appears after the system runs a while as ice melts; cooling may also feel weak	No, requires diagnosing why the coil froze
Dirty or clogged air filter	Restricts airflow, can trigger the coil to freeze	Yes, check and replace regularly
Cracked or full condensate drain pan	Water pools directly under the indoor unit even with a clear drain line	No, requires professional inspection
Improperly installed or sagging drain line	Slow or backed-up drainage even without an obvious clog	No, requires professional correction

Brand-Specific Notes

PLACEHOLDER, pending Ben's input. Reminder: for luxury or specialty HVAC brands, use "experience across [brand]" language only, never factory-certification claims.

How to Prevent This

✅

Replace the air filter regularly to maintain proper airflow across the coil

✅

Have the condensate drain line flushed periodically, often included in professional maintenance

✅

Schedule annual professional maintenance to catch early signs of restricted airflow

✅

If you see ice on the coil or lines, turn the system off and let it thaw before running it again

✅

Address a slow or intermittent drip early, before it leads to water damage

DIY vs. Call a Professional

Safe to Try Yourself

Replacing the air filter regularly
Turning the system off if you notice ice on the coil or lines
Flushing the drain line at its outdoor termination if it's easily accessible