AC Leaking Water: How to Fix It

Last updated: April 2026

By the HVAC Pricing Guide Team

If your AC is leaking water right now, you are probably dealing with a mess and worrying about damage to your floors, walls, or ceiling. The good news is that this is one of the most common AC problems, and in many cases you can fix it yourself within the next hour. The most important thing to do first is turn the system off. A leaking AC almost always means the condensate drain is clogged, and water that is not draining will keep coming until you stop the system. This guide walks you through exactly what to do right now, explains every possible cause of an AC water leak, tells you which repairs you can handle yourself and which require a technician, and covers the costs involved. All pricing data is independently researched with no affiliate relationships with any HVAC company.

For broader AC repair pricing, see our complete AC repair cost guide. For condensate drain line specifics, see our condensate drain line repair cost guide. If your AC has other symptoms beyond leaking water, try our HVAC troubleshooter tool to narrow down the problem.

What Should You Do Right Now?

If you are reading this because your AC is actively leaking water, follow these five steps before doing anything else. Acting quickly limits water damage and makes the eventual repair simpler.

Step 1: Turn the AC off at the thermostat

Switch the thermostat to OFF. Do not just raise the temperature setting, because the system may still cycle on. You need to stop the unit from running entirely so it stops producing condensate (the water that forms when your AC removes humidity from indoor air). As long as the system runs, it generates water, and if that water cannot drain properly, it will continue to overflow and leak.

Step 2: Turn off the system at the breaker

Go to your electrical panel and flip the breaker for the air handler (the indoor unit) to the OFF position. This ensures the system cannot accidentally restart and provides an extra layer of safety in case there is any water near electrical connections. The breaker for the air handler is typically labeled "AC," "Air Handler," "HVAC," or "Furnace" on the panel directory. If you are not sure which breaker controls the air handler, flip the one that corresponds to the area where the indoor unit is installed.

Step 3: Identify where the water is coming from

The location of the water leak tells you a lot about the cause. Look at the indoor air handler unit, which is typically located in a closet, attic, garage, or utility room. Check whether water is pooling directly under the unit, dripping from the ceiling (if the unit is in the attic), running along ductwork, or appearing at the base of the outdoor unit. Water pooling directly under the indoor unit points to a drain pan overflow, which usually means a clogged condensate drain line. Water dripping from the ceiling below an attic-mounted unit is the same problem but more urgent because the water has already saturated insulation and drywall. Water at the outdoor unit base is less concerning and often normal, but excessive pooling can indicate a problem.

Step 4: Place towels or a bucket to contain the water

While the system is off, the leak will slow down and eventually stop as the remaining condensate finishes draining (or stops being produced). However, there may be standing water in the drain pan or on surfaces above your living space. Place towels around the base of the indoor unit and position a bucket or large container under the most active drip point. If water is coming through the ceiling, place a bucket under the drip and consider poking a small hole in the center of any bulging drywall to let the water drain in a controlled manner rather than letting it spread horizontally and soak a larger area.

Step 5: Document the damage with photos

Take photos and video of the leak source, the water damage, any staining on ceilings or walls, and the area around the indoor unit. If the leak has been going on for more than a day or two and has caused visible damage, you may need to file a homeowners insurance claim. Insurance adjusters require documentation of the damage, and photos taken immediately after discovery are the strongest evidence. Include timestamps and capture both wide shots of the affected area and close-ups of any staining, warping, or discoloration.

Why Is a Clogged Condensate Drain Line the Most Common Cause?

A clogged condensate drain line is the number one reason ACs leak water, accounting for the majority of water leak service calls. Understanding what the condensate drain line does and why it clogs helps you both fix the current problem and prevent it from happening again.

What the condensate drain line does

When your AC cools indoor air, it also removes moisture from that air. Warm, humid air passes over the evaporator coil (the cold indoor coil where refrigerant absorbs heat), and the moisture in the air condenses on the coil surface, similar to how water droplets form on a cold glass of water on a hot day. This condensate water drips off the coil into a drain pan positioned directly below it. From the drain pan, the water flows through a PVC pipe, typically 3/4 inch in diameter, that routes to the outside of your home, a floor drain, or a utility sink. This PVC pipe is the condensate drain line. On a humid day, a residential AC system can produce 5 to 20 gallons of condensate water per day. All of that water needs somewhere to go, and the drain line is the only path.

Why the drain line clogs

The inside of the drain line is a dark, damp environment, which is exactly what algae and mold need to grow. Over weeks and months, a slimy biofilm builds up on the interior walls of the PVC pipe. Dust and dirt particles that pass through the air filter and land on the wet evaporator coil get washed into the drain pan and carried into the drain line, where they stick to the biofilm. Eventually, the buildup narrows the pipe enough to slow drainage, and then blocks it entirely. In humid climates, this process can happen in a single cooling season. In drier climates, it may take two or three seasons. But in every climate, it will eventually happen if the line is not maintained.

How to clear a clogged drain line yourself

Clearing the condensate drain line is one of the most accessible DIY AC repairs. You do not need specialized tools or technical knowledge, and the process takes 10 to 20 minutes. Here is how to do it.

First, locate the outdoor end of the condensate drain line. This is where the PVC pipe exits your home, usually near the foundation or close to the outdoor AC unit. It may be dripping water (or not, if the clog is preventing flow). Second, attach a wet/dry shop vacuum to the end of the drain line. You can use your hand to create a seal around the connection, or wrap a rag around the junction to tighten the fit. Run the shop vacuum for 60 to 90 seconds. The suction pulls the clog material out of the line and into the vacuum. You may hear the clog release as a gurgling sound. Third, go inside and locate the condensate drain access port, which is a T-shaped PVC fitting with a cap near the indoor air handler. Remove the cap and pour one cup of white distilled vinegar into the opening. The vinegar kills algae and mold inside the line and helps dissolve remaining debris. Fourth, wait 30 minutes, then pour a cup of warm water into the access port and check the outdoor end to confirm water is flowing through. If water flows out the outdoor end, you have successfully cleared the clog.

If you do not have a shop vacuum, you can try using a long, flexible brush or a plumber's snake inserted from the outdoor end to break up the clog mechanically. You can also try flushing the line from the indoor access port with warm water, though this is less effective on severe clogs because you are pushing the blockage rather than pulling it out.

What about the condensate pump?

Some homes, particularly those where the air handler is installed in a basement or below the level of the nearest drain, use a condensate pump instead of relying on gravity to move the water. A condensate pump is a small electric pump that sits near the air handler and actively pushes condensate water up and out to a drain location. If your system has a condensate pump and your AC is leaking water, the pump may have failed. Check whether the pump is receiving power, whether the float switch (a small arm that rises with the water level and activates the pump) is moving freely and not stuck, and whether the pump's discharge line is clogged or kinked. A failed condensate pump costs $50 to $150 to replace, plus $75 to $150 for labor if a technician installs it. See our condensate drain line cost guide for more details.

DIY success rate for drain line clogs

The shop vacuum method clears about 80% of condensate drain line clogs. It is the same technique many HVAC technicians use as their first step. If the clog is near the outdoor end of the line, the vacuum pulls it right out. If the clog is deeper in the line or if the line has multiple low points where debris accumulates, the vacuum may not generate enough suction to clear it. In those cases, a technician can use a nitrogen flush (high-pressure nitrogen gas blown through the line) or a specialized drain line cleaning tool to clear stubborn blockages. Professional drain line clearing costs $75 to $200.

How Does a Failing Drain Pan Cause AC Water Leaks?

The drain pan is the second most common cause of AC water leaks. The drain pan sits directly below the evaporator coil and catches all the condensate water before routing it to the drain line. When the pan itself fails, water bypasses the drain system entirely and leaks onto whatever surface is below the unit.

Primary drain pan failure

The primary drain pan is a shallow metal or plastic tray that is permanently attached to or integrated into the air handler unit. Metal drain pans, particularly those made of galvanized steel, rust over time because they are in constant contact with water. A rusted drain pan develops small holes or cracks that allow water to leak through the bottom of the pan rather than flowing to the drain line. Plastic drain pans can crack from age, UV exposure (in attic installations), or from being bumped during filter changes or other maintenance. If you see water leaking from the bottom of the air handler rather than overflowing from the top of the pan, the pan itself likely has a hole or crack.

The secondary (emergency) drain pan

Many installations, particularly attic-mounted air handlers, include a secondary drain pan underneath the entire unit as a safety catch. This secondary pan is a larger, shallower pan that sits under the air handler and has its own separate drain line. If you see water in the secondary pan, it means either the primary drain line is clogged (and water is overflowing the primary pan into the secondary pan) or the primary pan has a hole (and water is dripping through into the secondary pan). Either way, finding water in the secondary pan is a warning sign that the primary drainage system has failed and needs immediate attention. Some secondary pans have a float switch connected to them. The float switch (a device that detects rising water levels) automatically shuts the AC system off when the secondary pan fills with water, preventing overflow and water damage. If your system keeps shutting off for no apparent reason, check whether the secondary pan has water in it.

Drain pan replacement cost

Replacing a drain pan costs $200 to $500, including parts and labor. The cost depends on whether the pan is a standard universal size or a model-specific pan that must be ordered from the manufacturer. Attic installations cost more because of the difficulty of accessing the unit. Some older units have the drain pan welded or permanently integrated into the air handler body, making standalone replacement impossible. In those cases, the entire air handler section may need to be replaced, which costs significantly more. For units over 12 to 15 years old where the drain pan is integrated, this repair often tips the math toward full system replacement. See our when to replace your HVAC guide for help with that decision.

How Does a Frozen Evaporator Coil Cause Water Leaks?

A frozen evaporator coil is the third most common cause of AC water leaks, and it is the one that confuses homeowners the most. Ice forming inside your AC system seems counterintuitive, but it happens regularly and the resulting water when that ice melts can overwhelm the drainage system.

Why ice forms on the evaporator coil

The evaporator coil is the indoor component where liquid refrigerant (the chemical compound that carries heat out of your home) evaporates and absorbs heat from the air passing over it. Under normal conditions, the coil temperature stays around 35 to 40 degrees Fahrenheit, cold enough to cool the air but not cold enough to freeze the moisture on the coil. Two conditions cause the coil temperature to drop below freezing and allow ice to form.

The first and most common condition is restricted airflow. When the air filter is dirty, clogged, or has not been changed in months, it restricts the flow of warm air across the coil. Without enough warm air to absorb the cold from the refrigerant, the coil temperature drops below 32 degrees and moisture on the coil surface freezes. Closed or blocked supply vents, a failing blower motor, or collapsed ductwork can also restrict airflow enough to cause freezing. The second condition is low refrigerant. When the system is low on refrigerant due to a leak, the reduced amount of refrigerant in the coil expands more than it should, dropping the coil temperature below freezing. Low refrigerant also reduces the system's cooling capacity, so the system runs longer, giving ice more time to accumulate.

How the thaw causes a water leak

Ice on an evaporator coil does not stay small. Once freezing starts, ice builds on itself. The initial thin layer of frost insulates the coil from the passing air, causing the temperature to drop further and more ice to form. Left unchecked, the entire coil can encase in a solid block of ice that extends along the refrigerant lines back toward the outdoor unit. When the system cycles off (or when you turn it off after discovering the problem), all of that ice begins to melt. A heavily iced coil can produce several gallons of water as it thaws. The drain pan and drain line are designed to handle the normal condensate flow, which is a slow, steady drip. They are not designed to handle the sudden surge of water from a melting block of ice. The result is water overflowing the drain pan, flooding the area around the air handler, and potentially leaking through ceilings or into walls.

How to diagnose a frozen coil

Look for these signs. Ice is visible on the copper refrigerant lines (the two copper pipes that connect the indoor unit to the outdoor unit). The larger of the two lines, called the suction line, is insulated with black foam. If ice has formed, you may see frost or ice crystals on the insulation or on the exposed copper near the connection points. Ice may be visible on the evaporator coil itself if you can access it (remove the air handler panel to look). The system is blowing warm or lukewarm air instead of cold air. The system is running continuously without reaching the thermostat set point. Water is pooling under the indoor unit even though the drain line appears to be flowing.

How to fix a frozen evaporator coil

Step one: Turn the AC off at the thermostat. Do not just set it to a higher temperature. Turn it fully off. Step two: Set the fan setting on the thermostat to ON (not AUTO). This runs the blower fan continuously, circulating warm room air across the frozen coil to accelerate melting. If your thermostat does not have a fan-only setting, simply leaving the system off and allowing natural warming will work, but it takes longer. Step three: Check the air filter. If it is dirty, replace it immediately. A standard air filter costs $5 to $25 at any hardware store. Step four: Place towels and a bucket under the indoor unit to catch the meltwater. Step five: Wait 4 to 6 hours for the ice to melt completely. Do not try to chip or scrape ice off the coil, as you can damage the delicate aluminum fins. Step six: After the ice has fully melted and you have replaced the filter, restart the system and monitor it for 24 hours. If the coil freezes again, the problem is not the filter. You likely have a refrigerant leak, and you need a technician to diagnose and repair it.

The cost to diagnose and address a frozen coil ranges from $0 (if a filter change solves the problem) to $150 to $400 for a professional visit that includes refrigerant testing. If a refrigerant leak is found, repair costs climb to $200 to $1,500 depending on the leak location, plus the cost of a refrigerant recharge. For a detailed breakdown of evaporator coil repairs and replacement, see our evaporator coil cost guide.

What Other Problems Cause an AC to Leak Water?

While clogged drain lines, failing drain pans, and frozen coils account for the vast majority of AC water leaks, two additional causes are worth understanding, especially if the first three do not match your situation.

Disconnected drain line

The condensate drain line can become disconnected from the drain pan fitting, especially in attic installations where temperature extremes cause PVC pipes to expand and contract over years. Vibration from the air handler can also loosen push-fit connections over time. A disconnected drain line means condensate water pours directly out of the open pipe connection rather than flowing through the line to the outside. This cause is more common in homes where the air handler is in the attic and the PVC connections were not glued (cemented) during installation. If you can access the drain line where it connects to the drain pan, check that the connection is tight and that no gap exists between the pipe and the fitting. Reconnecting a drain line is a simple repair that costs $75 to $150 if a technician does it, or nothing if you can reach the connection and reattach the pipe yourself.

Improperly installed or unlevel unit

The air handler must be installed level, or very close to it, for condensate to flow correctly toward the drain pan outlet. If the unit is tilted away from the drain outlet, water pools on the opposite side of the pan and eventually overflows before it can reach the drain. This problem is most common after a new installation or after work has been done near the air handler that may have shifted its position. It can also occur when the platform or shelf supporting the unit sags over time from age or water damage. Checking whether the unit is level requires placing a bubble level on top of the air handler. If it is visibly tilted, the support structure needs to be adjusted. This is typically a $100 to $250 repair if a technician needs to re-level the unit and its support platform.

How Quickly Does Water Damage Get Serious?

Many homeowners underestimate how quickly a small AC water leak escalates into a costly problem. Understanding the timeline helps you grasp why this repair should not wait until next week or next month.

The first few hours

Within the first few hours of an active leak, water begins to stain ceiling drywall, creating visible discoloration that seeps outward from the drip point. Drywall absorbs water rapidly. A small drip from an attic-mounted air handler can create a visible brown or yellowish stain on the ceiling within 2 to 4 hours. Carpet and carpet padding in the area absorb water and begin to smell musty. Hardwood flooring begins to absorb moisture, which will eventually cause warping and buckling. At this stage, the damage is mostly cosmetic, and drying the area thoroughly may prevent permanent harm.

24 to 48 hours

This is the critical window. Mold spores (microscopic organisms that are present in every home and become active in damp conditions) begin colonizing damp surfaces within 24 to 48 hours if the temperature is between 60 and 80 degrees, which is typical in any air-conditioned home. Mold grows on drywall paper facing, wood framing, carpet backing, and insulation. Drywall that has been wet for 24 hours or more begins to lose structural integrity and may need to be replaced rather than simply dried and painted. Insulation in the attic or walls that absorbs water loses its thermal performance and becomes a breeding ground for mold.

One week and beyond

After a week of ongoing or repeated leaking, the damage compounds significantly. Drywall in the ceiling may begin to sag or bubble, and sections may need to be cut out and replaced. Wall cavities that have absorbed water develop hidden mold growth that is not visible from the living space but spreads behind the drywall. Subflooring (the structural layer beneath your visible floor) can begin to warp and weaken. Insulation that stays wet becomes matted and ineffective. The repair cost at this point is no longer about fixing the AC. It is about water damage restoration, which involves industrial fans, dehumidifiers, mold remediation, drywall replacement, and potentially flooring replacement.

The cost escalation

A clogged condensate drain line caught and cleared on day one costs $75 to $200. The same clog left for a week or two can result in ceiling drywall replacement ($500 to $1,500), insulation replacement ($300 to $800), mold remediation ($1,500 to $5,000 depending on the extent), and water damage restoration work ($1,000 to $3,000 or more). The total can easily reach $3,000 to $10,000 for what started as a $100 repair. The lesson is clear: a small leak today is a $5,000 ceiling repair next week if you ignore it.

Does Homeowners Insurance Cover AC Water Leak Damage?

Whether your homeowners insurance covers water damage from an AC leak depends on one key distinction: was the damage sudden or gradual?

Sudden and accidental damage (usually covered)

If a drain line breaks, a pipe connection fails unexpectedly, or a drain pan cracks and floods the area beneath it, most homeowners insurance policies cover the resulting water damage. The damage must be sudden, meaning it happened without warning and was not the result of ongoing neglect. The key word insurers use is "accidental." If you can show that the leak appeared without prior symptoms and you acted promptly to address it, the claim is more likely to be approved.

Gradual damage (usually not covered)

If the leak has been slowly dripping for weeks or months and you did not address it, most policies exclude the resulting damage under a "maintenance and neglect" clause. Insurance companies consider a slow, ongoing leak to be a maintenance issue that the homeowner should have caught and repaired. If the adjuster finds evidence that the leak was gradual (thick mold growth, heavily stained and warped drywall, multiple layers of water staining suggesting repeated wet-dry cycles), the claim may be denied. This is another reason to act quickly: a prompt response to a sudden leak supports an insurance claim, while a delayed response gives the insurer grounds to classify it as gradual.

The AC unit itself (usually not covered)

Homeowners insurance typically does not cover the cost of repairing the AC system itself. The drain line clearing, drain pan replacement, or evaporator coil repair is your responsibility. Insurance covers the collateral water damage to the home's structure and contents, not the mechanical failure that caused the damage. Your AC manufacturer's warranty or an extended home warranty may cover the unit repair, but that is separate from your homeowners insurance.

When Can You Fix an AC Water Leak Yourself?

Several AC water leak causes are well within a homeowner's ability to resolve without calling a technician. Here are the situations where a DIY fix is appropriate, effective, and safe.

Clogged condensate drain line

This is the most common cause and the most DIY-friendly repair. Use the shop vacuum method described earlier in this guide. Attach a wet/dry shop vacuum to the outdoor end of the drain line, run it for 60 to 90 seconds, then pour a cup of vinegar into the indoor access port. The entire process takes 10 to 20 minutes. If you do not have a shop vacuum, you can try flushing the line with warm water from the indoor access port, though this is less effective for solid clogs. A shop vacuum large enough for this task costs $30 to $60 at any hardware store and is useful for many household tasks beyond AC maintenance.

Clogged condensate trap

Some drain line configurations include a P-trap (a U-shaped bend in the PVC pipe, similar to the trap under a bathroom sink). The trap holds a small amount of water to prevent air from being sucked back through the drain line. Over time, algae and sludge accumulate in the trap and block flow. If your drain line has a trap, it is usually accessible near the indoor unit. Remove the trap section (it may be held by push-fit connections or glued joints), clean it thoroughly with a bottle brush and hot water, and reinstall it. If the joints are glued and you cannot remove the trap without cutting the pipe, a technician can replace it for $75 to $150.

Dirty air filter causing frozen coil

If you determine that a frozen evaporator coil is causing the water leak, and the cause is a dirty air filter, the fix is straightforward: turn the system off, replace the filter ($5 to $25), wait 4 to 6 hours for the ice to melt, and restart the system. No tools are needed beyond the replacement filter. Check the filter size printed on the existing filter frame before going to the store.

Minor level adjustment

If the air handler is slightly unlevel and you can access the unit's support platform, placing shims (thin wedges of wood or plastic) under the low side to re-level the unit is a simple fix. Use a bubble level to verify the unit is level after shimming. This only applies to units mounted on a shelf, stand, or platform that you can easily access. Do not attempt to adjust a unit that is suspended from ceiling joists or mounted in a difficult-to-reach attic location.

When Do You Need to Call a Professional?

Some AC water leak situations require professional diagnosis and repair. Attempting these yourself risks making the problem worse, voiding your warranty, or creating safety hazards.

Water in the secondary (emergency) drain pan

If the secondary drain pan beneath the air handler has water in it, the primary drainage system has failed at some point, whether the drain line, the primary pan, or the connections between them. While you can clear the primary drain line yourself, the fact that the secondary system activated means you should have a technician inspect the entire drainage setup to determine exactly what failed and whether the primary pan has a hole or crack that needs replacement.

Frozen evaporator coil that refreezes after filter replacement

If you replaced the filter, waited for the coil to thaw, restarted the system, and ice formed again within 24 to 48 hours, the problem is not airflow restriction. The most likely cause is low refrigerant from a leak. Refrigerant leak detection and repair requires EPA Section 608 certification, specialized equipment (electronic leak detectors, nitrogen pressure testing, manifold gauge sets), and technical expertise. Handling refrigerant without certification is both illegal and dangerous. A technician will locate the leak, repair it, pressure-test the system, evacuate any moisture and air from the lines, and recharge with the correct amount of refrigerant. See our AC repair cost guide for refrigerant recharge pricing.

Unit is 12 or more years old

If your AC system is older than 12 years and is leaking water, the underlying cause may be a deteriorating drain pan that is integrated into the air handler (not replaceable as a standalone part), corroded or damaged evaporator coil fins that disrupt normal condensate flow, or general system wear that makes the current repair one of several that will be needed in the near future. A technician can assess the overall condition of the system and help you decide whether the leak repair is a worthwhile investment or whether the repair cost is better applied toward a new system. Use our HVAC cost calculator to estimate replacement costs for your home.

Water in walls or ceiling

If water has penetrated into wall cavities or has been dripping through the ceiling for more than a day, you need both an HVAC technician to fix the leak source and a water damage restoration professional to assess and dry the affected areas. Drying wall cavities requires industrial equipment (high-velocity air movers, commercial dehumidifiers, and moisture meters to verify that hidden surfaces are dry). Attempting to address significant water intrusion with household fans and towels alone leaves moisture trapped in wall and ceiling cavities, which leads to mold growth. For emergency water damage situations, see our HVAC emergency repair guide.

Visible mold near the unit

If you can see mold growth on surfaces near the air handler, on the walls or ceiling near the leak, or inside the drain pan, the leak has been occurring long enough for mold to colonize. While surface mold on hard, non-porous surfaces like metal drain pans or PVC pipes can be cleaned with a household solution, mold on drywall, wood, carpet, or insulation typically requires professional remediation. A mold remediation professional can assess whether the mold is limited to visible surfaces or has spread into hidden areas behind walls and above ceilings.

What Should You Know About Mold From an AC Leak?

Mold is the most significant secondary consequence of an AC water leak that goes unaddressed for more than a day or two. Understanding how mold develops and what it means for your home helps you make informed decisions about how urgently to respond.

How quickly mold grows from an AC leak

Mold spores are present in virtually every indoor environment. They are microscopic and float in the air constantly. What keeps mold from growing on every surface in your home is the absence of sufficient moisture. When an AC leak creates a persistently damp surface, mold spores that land on that surface have the moisture they need to germinate and begin growing. In conditions between 60 and 80 degrees with sustained moisture, visible mold colonies can appear within 24 to 48 hours. Behind walls and above ceilings, where air circulation is poor and drying is extremely slow, mold grows even faster because the moisture lingers longer.

Where mold develops from AC leaks

The most common locations for mold growth from AC water leaks include the backside of ceiling drywall above the stain (invisible from the living space until the drywall is removed), inside wall cavities where water has run down from an attic unit, on the paper facing of drywall (the thin paper layer on the surface of drywall is an excellent food source for mold), on insulation that has absorbed condensate water, inside the drain pan and around the evaporator coil housing, and on carpet pad beneath any visible water pooling. Because much of this mold growth is hidden, a musty smell near the indoor unit or in the area below an attic-mounted system is often the first indication that mold has developed.

Health implications

Mold exposure affects different people differently. Common reactions include nasal congestion, throat irritation, coughing, eye irritation, and skin rash. People with asthma, allergies, or compromised immune systems may experience more severe reactions. The presence of mold in an HVAC system is particularly concerning because the system circulates air throughout the entire home, distributing mold spores to every room. If household members develop respiratory symptoms that improve when they leave the home and return when they come back, mold in or near the HVAC system is a possible cause.

Mold remediation costs

Small areas of surface mold (less than 10 square feet on hard surfaces) can be cleaned by a homeowner using appropriate cleaning products and protective equipment (gloves, N95 respirator mask, eye protection). Larger areas, mold on porous surfaces like drywall and insulation, or mold in hidden locations like wall cavities require professional remediation. Professional mold remediation costs $1,500 to $5,000 or more depending on the extent and location of the growth. This cost is in addition to repairing the AC leak that caused the moisture problem in the first place. The cost comparison makes the case for quick action: fixing a $100 drain line clog today prevents a $3,000 mold remediation next month.

How Do You Prevent Your AC From Leaking Water?

Preventing AC water leaks is straightforward and inexpensive compared to dealing with the consequences of an unaddressed leak. These maintenance steps take minimal time and cost and dramatically reduce your risk of a condensate-related water leak.

Pour vinegar down the drain line monthly

Once a month during the cooling season, pour one cup of white distilled vinegar into the condensate drain access port near the indoor unit. The vinegar kills algae and mold growth inside the drain line before it can form a clog. This is the single most effective preventive measure for the most common cause of AC water leaks. Set a recurring reminder on your phone for the first of each month during the months you run your AC. A gallon of white vinegar costs about $3 and lasts an entire cooling season.

Install a float switch on the drain line

A float switch, also called a condensate overflow switch or a wet switch, is a safety device that detects when water in the drain pan rises above the normal level. When triggered, the float switch shuts off the AC system, preventing water from overflowing and causing damage. Many building codes now require float switches on attic-mounted air handlers, but older installations may not have one. Adding a float switch costs $50 to $100 for the part and $75 to $150 for professional installation, or you can install it yourself if you are comfortable with basic wiring (the switch connects to the thermostat's Y terminal to interrupt the cooling call). A float switch does not prevent clogs, but it prevents clogs from causing water damage by shutting the system down before overflow occurs. This $50 to $100 investment can prevent thousands of dollars in water damage.

Change the air filter regularly

A clean air filter maintains proper airflow across the evaporator coil, which prevents the coil from freezing and the subsequent flood of meltwater when the ice thaws. Replace your filter every 30 to 60 days during the cooling season. In homes with pets, multiple occupants, or high dust levels, every 30 days is recommended. In single-occupant homes with low dust, every 60 days is typically sufficient. Set a reminder on your phone or purchase a year's supply of filters so the replacement is always on hand. For more on how maintenance prevents costly repairs, see our HVAC maintenance cost guide.

Schedule an annual tune-up

A professional AC tune-up includes clearing the condensate drain line, inspecting the drain pan for cracks or corrosion, checking the evaporator coil condition, verifying refrigerant levels, and testing airflow. Having a technician perform this inspection once a year, ideally in spring before the cooling season begins, catches developing problems before they cause a leak. A tune-up costs $75 to $200 and addresses all of the most common water leak causes in a single visit. See our AC tune-up cost guide for details on what a tune-up includes and what it should cost.

Inspect the drain pan annually

During your tune-up or on your own, visually inspect the primary drain pan for rust, cracks, or standing water. A thin film of water in the pan is normal (it is in the process of draining), but standing water that is not draining indicates a partial clog. Rust spots or visible corrosion on a metal pan mean the pan is deteriorating and will eventually develop a leak. Catching a corroding pan early lets you schedule a replacement on your terms rather than discovering it when water is pouring through your ceiling.

Keep the area around the outdoor unit clean

While most AC water leaks originate at the indoor unit, the outdoor end of the condensate drain line can also become blocked by dirt, mulch, insect nests, or debris pushed against the pipe opening. Check the outdoor termination point of the drain line periodically and make sure it is clear and draining freely. Some homeowners attach a small piece of mesh or screen over the outdoor opening to keep insects out while still allowing water to flow.

What Will the Technician Do When They Come Out?

Knowing what a professional AC water leak repair visit involves helps you evaluate whether the technician is being thorough and whether the diagnosis and pricing are reasonable.

Initial assessment

The technician will start by asking you questions: when did the leak start, where is the water appearing, how much water is there, has this happened before, and when was the system last serviced? They will then inspect the area around the indoor unit, the drain pan, and the drain line connections. If the unit is in the attic, they will go up and inspect the installation, the secondary drain pan, and the condition of the surrounding area including any water damage to framing or insulation.

Drain line clearing and testing

The most common repair is clearing the condensate drain line. The technician will use a shop vacuum, nitrogen flush, or a specialized CO2 drain gun (a tool that fires a burst of compressed gas through the line to blast out the clog) to clear the line. After clearing, they will pour water into the drain pan and confirm it flows freely through the line and exits at the outdoor end. They may also apply a biocide treatment (a chemical agent that prevents biological growth) to the drain line and drain pan to inhibit future algae and mold growth.

Refrigerant check

If the technician suspects a frozen evaporator coil contributed to the leak, they will connect manifold gauges to the system's service ports and measure the refrigerant pressure. Low pressure indicates a refrigerant leak. The technician may also measure the temperature split (the difference between the air temperature entering the return and the air temperature leaving the supply) to verify the system is cooling properly. A normal temperature split is 15 to 20 degrees. A split below 12 to 14 degrees suggests low refrigerant or another issue affecting cooling performance.

Evaporator coil inspection

The technician should visually inspect the evaporator coil for signs of ice damage, corrosion, or dirt buildup. A dirty coil reduces efficiency and can contribute to drainage problems because debris on the coil mixes with condensate and flows into the drain, accelerating clog formation. If the coil is dirty, the technician may recommend a coil cleaning, which costs $100 to $300 and involves applying a chemical cleaner and rinsing the coil. For detailed coil replacement pricing, see our evaporator coil cost guide.

Drain pan inspection and replacement

The technician will check both the primary and secondary drain pans for cracks, corrosion, and proper drainage. If the primary pan is rusted through or cracked, they will recommend replacement. They should also verify that the secondary pan's drain line is clear and that any float switch is functioning correctly. If no float switch is installed and your unit is attic-mounted, a good technician will recommend adding one.

System test

After completing the repair, the technician will restart the system and run it for 15 to 20 minutes to verify proper operation. They should confirm that condensate is flowing through the drain line, that the system is producing cold air within the normal temperature split range, and that no new leaks appear. Ask the technician to show you where the drain line access port is and explain the monthly vinegar maintenance routine so you can prevent future clogs yourself.

How Much Does It Cost to Fix an AC Water Leak?

The cost to fix an AC water leak varies significantly depending on the cause. Here is a breakdown of every common repair associated with AC water leaks, from the simplest to the most complex.

These costs cover the AC repair itself. If the leak has caused secondary damage, additional costs apply. Ceiling drywall repair runs $500 to $1,500 depending on the area affected. Insulation replacement costs $300 to $800. Mold remediation ranges from $1,500 to $5,000 or more depending on the extent and location of the growth. Full water damage restoration, including industrial drying, material removal, and rebuilding, costs $1,500 to $5,000 or more for a significant event. The gap between a $100 drain line clearing and a $5,000 water restoration job is entirely determined by how quickly you respond. For a broader look at AC repair pricing, see our complete AC repair cost guide. To see if your AC is worth repairing at all, try our HVAC cost calculator.

If your AC is not cooling in addition to leaking water, the two problems may be connected. A frozen evaporator coil causes both symptoms simultaneously. See our AC not cooling guide for additional troubleshooting steps.

Frequently Asked Questions About AC Water Leaks