Why Is My AC Leaking Water? Chicago Homeowner Guide

Published: May 3, 2026 · By SAVA HVAC & Appliance Repair

Finding water under your air handler or a puddle around your indoor unit is unsettling — and if ignored, it can cause real damage to ceilings, drywall, and flooring. The good news is that most AC water leaks have a straightforward cause. Here are the six most common reasons a Chicago AC leaks water, and what to do about each one.

1. Clogged Condensate Drain Line

This is the #1 cause of AC water leaks in Chicago homes. As your AC cools the air, it pulls moisture out of it — that moisture (condensate) drips into a drain pan and flows out through a PVC drain line. Over time, algae, mold, and debris build up inside that line and block it. When blocked, water backs up in the pan and overflows onto your floor or ceiling.

DIY fix: Locate the condensate drain line — usually a white PVC pipe near the indoor air handler — and place a wet/dry vacuum over the end. Run it for 1–2 minutes to suction out the clog. Pour a cup of distilled white vinegar into the access port (a capped T-fitting near the unit) every few months to prevent algae buildup.

2. Frozen Evaporator Coil Thawing

If your AC has been running but struggling to cool, ice may have built up on the evaporator coil inside the air handler. When the system shuts off — or you notice the problem and turn it off — that ice melts and drips down, overwhelming the drain pan. You'll often see ice on the copper refrigerant lines leading to the indoor unit, or feel reduced airflow from your vents.

What to do: Turn the AC off and switch the fan to ON (not AUTO) to let the coil thaw over 1–2 hours. Replace the air filter. Once thawed, have a technician check why it froze — the cause is almost always a dirty filter, low refrigerant, or a failing blower motor.

3. Cracked or Overflowing Drain Pan

There are typically two drain pans in a central AC system — a primary pan directly under the evaporator coil, and a secondary (overflow) pan below. Over years of use, plastic pans can crack and leak even when the drain line is clear. You may also have a rusted metal primary pan with a pinhole leak. If the drain line is clear but water is still pooling, inspect both pans for cracks, rust, or holes.

Fix: A cracked pan usually requires replacement. This is a technician job, as it involves removing access panels and, in some cases, partially lowering the air handler.

4. Low Refrigerant Causing Coil Freeze

Refrigerant doesn't deplete on its own — if your system is low on refrigerant, it means there's a leak somewhere in the refrigerant circuit. Low refrigerant causes the evaporator coil to drop below freezing, ice builds up, and eventually that ice melts and drips. Signs of a refrigerant leak include warm air from the vents, a hissing or bubbling sound near the refrigerant lines, and ice forming on the outdoor unit.

Fix: Refrigerant leaks require an EPA 608 certified technician to locate the leak, repair it, and recharge the system to the correct level. Do not just "top off" refrigerant — the leak will cause it to run low again within weeks.

5. Dirty Air Filter Blocking Airflow

A clogged filter restricts the warm air that flows over the evaporator coil. Without enough warm air moving across it, the coil gets too cold and freezes. This is the most preventable cause of AC leaks — and the fix is a $5 filter replacement. Check your filter now: if you can't see light through it when held up to a window, replace it. Filters in Chicago homes typically need replacement every 1–3 months in summer when AC runs constantly.

6. Improper Installation or Disconnected Drain Line

If you recently had HVAC work done and the leak started shortly after, the condensate drain line may have been reconnected incorrectly or is sagging in a way that prevents proper drainage. A drain line needs a continuous downward slope to let gravity move the water out. If there's a low spot in the middle of the line, water sits there and backs up. A technician can re-slope or re-route the line properly.

When to Turn It Off and Call a Pro

Turn the AC off and call a technician if:

• Water is dripping through a ceiling or along walls (risk of drywall damage and mold)
• You've cleared the drain line but water returned within a day or two
• The leak is accompanied by warm air from vents (likely refrigerant issue or coil freeze)
• You see or hear ice forming anywhere on the system
• The drain pan is cracked or rusted through

A clogged drain line is easy to ignore in spring — but when Chicago hits 95°F in July and your AC runs 18 hours a day, that small clog becomes an emergency. SAVA offers same-day AC diagnosis throughout Chicago and suburbs.

Frequently Asked Questions

Is it normal for an AC to drip water?

A small amount of condensation dripping from the outdoor unit is normal on humid days. Water dripping inside your home or pooling under the indoor air handler is not normal and should be addressed promptly to prevent water damage and mold growth.

Can I run my AC if it's leaking water?

No. Turn the system off if it's actively dripping inside. Running it while leaking can cause water damage to ceilings, walls, and floors, and can promote mold growth. If the leak is from a frozen coil, running the system makes the freeze worse and risks compressor damage.

How do I unclog my AC drain line?

Place a wet/dry vacuum over the end of the condensate drain line (outside your home) and run it for 1–2 minutes. You can also pour a cup of distilled white vinegar into the access port near the indoor unit to break up algae. If water still won't drain after this, the clog may be deeper — call a technician.

Why is my AC freezing up and leaking water?

A frozen AC coil is usually caused by a dirty air filter restricting airflow, low refrigerant from a leak, or a failing blower motor. When the ice melts, it drips from the indoor unit. Turn the system off, switch the fan to ON to thaw it, replace the filter, then call a technician to check refrigerant and airflow.