Why does my AC unit drip water?

An air conditioner removes humidity from indoor air as part of the cooling process. Warm, humid air passes over the evaporator coil, which is cold enough to cause the moisture in the air to condense — the same way a cold glass of water sweats on a humid day. This condensation drips into a drain pan and flows out through the condensate drain line. When the system is working correctly, you should see a small amount of water dripping from the exterior drain line. Water appearing in unexpected places — on the floor inside, on the ceiling, or pooling around the air handler — means the drainage system is blocked or damaged.

How do I clean the condensate drain line?

The simplest method is a vinegar flush: locate the condensate drain access port on the air handler (a capped T-fitting on the drain line), pour one cup of white vinegar into it, and let it sit for 30 minutes before flushing with water. For a more stubborn clog, use a wet-dry vacuum at the exterior end of the drain line — hold the vacuum hose against the drain opening and run it for 2 to 3 minutes to pull the clog out. Repeat the vinegar treatment every three months as preventive maintenance.

Can I replace a cracked AC drain pan myself?

On most air handlers, the primary drain pan — the one directly under the evaporator coil — is a sealed component that requires partial disassembly of the air handler to access. This is typically a job for an HVAC technician. The secondary drain pan, which sits under the entire air handler unit and catches overflow, is a separate plastic tray that is straightforward to replace yourself. It slides or lifts out, and a replacement pan of the same dimensions drops in. A temporary patch with epoxy putty can stop a small crack in the secondary pan while you wait for a replacement.

Can a refrigerant leak cause water to drip from the AC?

Yes, indirectly. Low refrigerant causes the evaporator coil to get colder than designed — sometimes cold enough to freeze. When the ice that has built up on the coil melts, it produces far more water than the drain pan can handle and overflows onto the floor. Signs that a refrigerant issue is causing the leak include ice visible on the refrigerant lines or on the indoor coil, reduced cooling performance even though the unit runs constantly, and a hissing or bubbling sound near the indoor unit. If you suspect low refrigerant, shut the system off and call an HVAC technician — adding refrigerant requires a license and specialized equipment.

What is the difference between an inside leak and an outside leak on an AC unit?

Water dripping from the outdoor condenser unit during cooling is normal — it is condensation from the coil and drain from the defrost cycle on heat pumps. Water appearing inside the home — under the air handler, on the ceiling near a ceiling cassette, or dripping from supply vents — always indicates a problem. Inside leaks are caused by a clogged condensate drain, cracked drain pan, frozen coil, or improper unit installation angle. Outside leaks that are heavier than a normal drip may indicate a dirty coil or a blocked drain port on the condenser.

How do I know if my AC drain pan is cracked?

Empty the standing water from the drain pan with a wet-dry vacuum, dry the pan with rags or towels, and inspect it with a flashlight. Cracks often appear as dark hairline splits along the bottom corners or sides of the pan. Pour a small amount of water into the dry pan and watch for drips below — this confirms an active crack even if you cannot see it clearly. Rust stains radiating from a single point also indicate water has been seeping through a crack for some time.

How to Fix a Leaking AC Unit: Condensate Line, Drain Pan, and Refrigerant

Water in the wrong place is one of the most common AC complaints. The good news is that most AC leaks are condensate drainage problems — a clogged line or a cracked pan — that you can diagnose and fix without calling a technician.

This guide walks through each cause in order of likelihood, starting with the most common fix.

What You Need

Condensate drain pan tablets — slow-dissolve tablets that prevent algae and mold in the drain line
Wet-dry vacuum for condensate line — pulls clogs from the exterior drain opening
Mini split condensate pump — actively removes condensate when gravity drainage is not possible
AC coil cleaner spray — no-rinse formula for cleaning the evaporator coil
HVAC secondary drain pan — replacement overflow pan for under the air handler
Condensate drain pipe PVC fittings — for repairing or rerouting the drain line

Diagnose the Location First

Before grabbing a bucket, determine where the water is coming from. The location tells you the cause.

Water under the indoor air handler: The condensate drain pan is overflowing. This is almost always a clogged condensate drain line or a cracked pan.

Water dripping from supply vents or ceiling registers: The evaporator coil has frozen and is now thawing. This points to restricted airflow (a dirty filter) or low refrigerant.

Water on the floor near the air handler that appears when the AC is off: The secondary drain pan has been holding overflow and you only notice it when you look. Run the AC, watch where the dripping originates.

Water outside near the condenser: Normal in most cases. The condenser coil drips condensation. Puddles larger than a foot across during normal operation may indicate a dirty coil or blocked drain port.

Fix: Clogged Condensate Drain

This is the most common cause of AC water leaks. Algae, mold, and dust accumulate in the drain line over time and eventually block flow.

Bleach or vinegar flush:

Locate the condensate drain access port — a capped white PVC T-fitting on the drain line near the air handler.
Turn off the AC at the thermostat.
Pour one cup of white vinegar or a 50/50 bleach-water mix into the port.
Wait 30 minutes.
Flush with a cup of plain water.
Drop in one or two condensate drain pan tablets for ongoing prevention.

Wet-dry vacuum method (for full clogs):

Go to the exterior drain line termination — typically a 3/4-inch PVC stub outside the foundation or through the soffit.
Hold a wet-dry vacuum hose tightly against the opening or use a rubber adapter to seal the connection.
Run the vacuum for 2 to 3 minutes. This pulls the clog out from the exterior end.
Return inside and flush with vinegar as described above.

Fix: Cracked Drain Pan

A cracked secondary drain pan is easy to diagnose and replace.

Shut off the AC.
Vacuum out any standing water from the pan.
Dry the pan with rags.
Inspect with a flashlight for cracks, especially in the corners and at the drain opening.
To confirm, pour a cup of water in the dry pan and watch for drips below.

If the secondary pan is cracked, measure its dimensions and order a replacement of the same size. The pan lifts out from under the air handler. Slide the replacement in and ensure the drain fitting lines up with the drain line opening.

For a cracked primary pan — inside the air handler directly under the coil — call an HVAC technician. Accessing that pan requires disassembling the air handler cabinet.

When It Is Refrigerant

A refrigerant-related leak follows a specific pattern:

The AC runs constantly but the house does not cool adequately.
You can see ice on the refrigerant lines, on the coil inside the air handler, or on the outdoor unit.
When the ice melts — typically when the system is turned off or when the refrigerant is so low that the compressor cycles off — large amounts of water overflow the drain pan.
There may be a hissing or gurgling sound near the indoor unit.

If you see ice on the system, shut the AC off immediately and let it thaw fully (this takes 2 to 24 hours depending on how much ice has built up). Do not restart the system until the ice is completely melted. Call an HVAC technician to check refrigerant levels and locate the leak. Adding refrigerant without fixing the leak is not a lasting repair.

⏰ PT2H 💰 $10–$50 🔧 Plunger, Drain snake or auger, Bucket, Rubber gloves, Plumber putty or wax ring

Diagnose the Location First
Before grabbing a bucket, determine where the water is coming from. The location tells you the cause.
Fix: Clogged Condensate Drain
This is the most common cause of AC water leaks. Algae, mold, and dust accumulate in the drain line over time and eventually block flow.
Fix: Cracked Drain Pan
A cracked secondary drain pan is easy to diagnose and replace.
When It Is Refrigerant
A refrigerant-related leak follows a specific pattern:

How to Fix a Leaking AC Unit: Condensate Line, Drain Pan, and Refrigerant

What You Need

Diagnose the Location First

Fix: Clogged Condensate Drain

Fix: Cracked Drain Pan

When It Is Refrigerant

Free: 10-Point Home Maintenance Checklist

Save this for next time.

How to Fix a Leaking AC Unit: Condensate Line, Drain Pan, and Refrigerant

What You Need

Diagnose the Location First

Fix: Clogged Condensate Drain

Fix: Cracked Drain Pan

When It Is Refrigerant

Related Reading

Free: 10-Point Home Maintenance Checklist

Save this for next time.