Why Is My AC Leaking Water Inside? Common Causes & Fixes
You walk past your air handler in the basement and notice a puddle forming on the floor. Or maybe you spot water dripping from your ceiling vent in Sterling Heights. Either way, your AC is leaking water inside your home—and it needs attention now.
Here in Southeast Michigan, we see this problem constantly during summer. The combination of our humid climate (often 60-80% humidity in July and August) and aging HVAC systems creates the perfect conditions for condensate drainage issues. The good news? Most AC water leaks have straightforward causes, and many can be prevented with basic maintenance.
I've been diagnosing these issues across Macomb, Oakland, and St. Clair counties for years. In this post, I'll walk you through exactly why your AC is leaking water inside, what you can check yourself, and when to call a professional. No fluff—just the technical reality of what's happening in your system.
How Your AC Removes Moisture (And Where It Can Go Wrong)
Before we get into specific problems, you need to understand what's supposed to happen. Your air conditioner doesn't just cool air—it also removes moisture from it. That's why your home feels less humid when the AC runs.
Here's the process: Warm, humid air from your home passes over the cold evaporator coil inside your air handler. When that warm air hits the cold coil (typically running at 40-45°F), moisture condenses on the coil surface—just like water beads form on a cold glass of iced tea on a humid Michigan afternoon.
That condensed water drips into a metal or plastic drain pan positioned directly beneath the evaporator coil. From there, it flows through a condensate drain line—usually a ¾-inch PVC pipe—that carries the water outside your home or to a floor drain in your basement.
On a typical humid Michigan summer day, a residential AC system can produce 5-20 gallons of condensate water per day. That's a lot of water moving through a small pipe. When any part of this drainage system fails, that water ends up on your floor, ceiling, or walls instead of outside where it belongs.
7 Common Causes of Indoor AC Water Leaks
After diagnosing hundreds of AC water leaks across Metro Detroit, I can tell you these seven issues account for about 95% of the cases we see. Let's break down each one.
1. Clogged Condensate Drain Line (The Most Common Culprit)
This is the number one cause—probably 60% of the AC water leaks we service in Macomb County trace back to a clogged drain line. Over time, algae, mold, dust, and debris accumulate inside that PVC condensate line. In Michigan's humid climate, algae growth is particularly aggressive.
The drain line runs from your air handler to the outside of your home (or to a floor drain). It's usually ¾-inch PVC, and it only takes a small blockage to stop water flow completely. When the line clogs, water backs up into the drain pan, overflows, and leaks into your home.
You'll often see this problem spike in June and July when AC usage ramps up after months of sitting dormant. The stagnant water in the line during spring creates perfect conditions for algae to form a blockage.
2. Frozen Evaporator Coil
If your evaporator coil freezes over, you'll eventually have a water leak—because when that ice melts, it produces far more water than the drain pan can handle. The water overflows and leaks out.
Coils freeze for several reasons: a severely dirty air filter restricting airflow, low refrigerant levels (often from a leak), a malfunctioning blower motor, or closed/blocked supply vents throughout your home. When airflow across the coil drops below a certain threshold, the coil temperature can drop below freezing, and ice builds up.
If you see ice on your evaporator coil or refrigerant lines, turn off your AC immediately and call a professional. Running the system with a frozen coil can damage the compressor—a repair that costs $1,200-$2,500. This is related to issues we commonly see with air conditioning repair in Mount Clemens, where frozen coils often stem from neglected maintenance.
3. Cracked or Overflowing Drain Pan
The drain pan sits directly under your evaporator coil. Most systems actually have two pans: a primary pan (often built into the air handler) and a secondary overflow pan positioned beneath it as a backup.
These pans are typically made of metal or plastic. Metal pans rust over time, especially in humid basement environments common in Michigan homes. Plastic pans can crack due to age, temperature stress, or physical damage during maintenance.
If the primary drain line clogs and the primary pan cracks, water bypasses the secondary pan entirely and leaks directly onto your floor or ceiling below. In older systems (15+ years), cracked drain pans are extremely common.
4. Dirty Air Filter Restricting Airflow
A clogged air filter reduces airflow across the evaporator coil. When airflow drops, the coil gets too cold, which can lead to freezing (see cause #2). But even before the coil freezes completely, reduced airflow causes excessive condensation that overwhelms the drain system.
This is the easiest problem to prevent. Yet we routinely find homeowners in Royal Oak and Troy running AC systems with filters that haven't been changed in 6-12 months. A standard 1-inch pleated filter should be replaced every 30-60 days during cooling season.
If you have pets, smoke indoors, or run your AC constantly during Michigan's humid summers, you're on the 30-day schedule. Period. For more on how regular filter changes impact system performance, see our post on how an AC tune-up improves your home's air quality.
5. Low Refrigerant Levels
Your AC system is a sealed loop. If refrigerant levels are low, it's because there's a leak somewhere—refrigerant doesn't just "run out" like gasoline in a car. Low refrigerant causes the evaporator coil to run too cold, which leads to ice formation and eventual water leaks when that ice melts.
You might also notice these symptoms alongside the water leak: the AC runs constantly but doesn't cool effectively, ice on the refrigerant lines outside, or hissing sounds near the indoor or outdoor unit. Refrigerant leaks require professional repair—this isn't a DIY fix, and it's illegal for unlicensed individuals to handle refrigerant under EPA Section 608 regulations.
6. Improper AC Installation or Leveling
The air handler and drain pan must be installed level—or with a slight pitch toward the drain line—so gravity can move condensate water out of the system. If the unit was installed improperly or has settled over time (common in homes with shifting foundations or basement floor settling), water pools in the pan instead of draining.
We see this frequently in older Michigan homes where the original installation was rushed or done by an unlicensed contractor. The air handler might be tilted backward, causing water to pool at the back of the pan where there's no drain outlet. Eventually, the pan overflows.
Fixing this requires physically releveling the air handler—not complicated, but it requires a professional to ensure proper pitch and secure mounting.
7. Disconnected or Damaged Drain Line
Sometimes the drain line simply comes loose from the drain pan or air handler connection. This happens more often than you'd think, especially after someone performs maintenance and doesn't fully reconnect the line, or if the PVC connections weren't properly glued during installation.
We also see drain lines that have been damaged by rodents, crushed by storage items in the basement, or cracked due to freezing (if the line runs through an unheated space). A visual inspection of the entire drain line path usually reveals these issues quickly.
What You Can Check Yourself Before Calling a Tech
Not every AC water leak requires an immediate service call. Here's what you can safely check on your own before contacting a reliable HVAC contractor in Metro Detroit.
Step 1: Turn Off Your AC System
First, switch your thermostat to OFF—not just to a higher temperature, but completely off. Then go to your electrical panel and turn off the circuit breaker that powers the air handler. This is a safety precaution. You're going to be working near electrical components and water, which is a dangerous combination.
Step 2: Check and Replace Your Air Filter
Locate your air filter (usually in a return air grille or at the air handler itself). Pull it out and hold it up to a light. If you can't see light passing through easily, it's clogged and needs replacement. Install a new filter with the airflow arrow pointing toward the air handler.
Use a MERV 8-11 rated pleated filter for most residential systems. Avoid the cheap fiberglass filters—they don't filter effectively. Also avoid MERV 13+ filters unless your system was specifically designed for them; high-MERV filters can restrict airflow on standard residential systems.
Step 3: Inspect the Drain Pan
Locate the drain pan beneath your evaporator coil. You might need a flashlight. Look for standing water, cracks, rust holes, or algae growth. If the pan is full of water but the drain line isn't clogged, the pan itself might be damaged or the system isn't level.
If you see standing water, you can carefully remove it with a wet/dry vacuum or towels. But don't just clean it up and forget about it—you need to identify why the water isn't draining.
Step 4: Check the Condensate Drain Line
Follow the drain line from the air handler to where it exits your home (or connects to a floor drain). Look for obvious disconnections, cracks, or kinks in the line. Check the end of the line outside—is water flowing out when the AC runs? If not, the line is likely clogged.
You can attempt to clear a simple clog by pouring a cup of distilled white vinegar into the drain line access port (usually a PVC tee fitting with a cap near the air handler). Let it sit for 30 minutes, then flush with water. For stubborn clogs, you'll need a professional with a wet/dry vacuum or specialized tools.
Safety Warning: Never use chemical drain cleaners (like Drano) in your AC condensate line. These products can damage PVC pipes and create toxic fumes when mixed with condensate water. Stick with vinegar or call a professional.
Step 5: Look for Ice on the Evaporator Coil
If you can access your evaporator coil (it's usually behind a metal panel on the air handler), look for ice buildup. If you see ice, turn off the system and let it thaw completely—this can take 4-8 hours. Once thawed, replace the filter and turn the system back on. If ice returns within 24 hours, you have a deeper problem (likely low refrigerant or a blower motor issue) and need professional diagnosis.
When to Call a Professional HVAC Technician
Some AC water leak scenarios require professional expertise and tools. Here's when to call a licensed technician instead of attempting DIY fixes.
You Suspect a Refrigerant Leak
If your evaporator coil keeps freezing even after you've replaced the filter and confirmed good airflow, you likely have low refrigerant due to a leak. Refrigerant leaks require EPA-certified technicians with specialized equipment to locate the leak, repair it, and recharge the system with the correct refrigerant type and quantity.
Refrigerant work is regulated by federal law. Only licensed, EPA Section 608-certified technicians can legally handle refrigerant. At NEXT Heating & Cooling, all our technicians carry EPA 608 certification and use electronic leak detectors to pinpoint even small leaks that aren't visible.
The Drain Pan Is Cracked or Rusted Through
Replacing a drain pan requires partially disassembling the air handler to access the pan beneath the evaporator coil. This isn't a simple swap—the coil often needs to be temporarily lifted, refrigerant lines must be protected, and the new pan must be properly sealed and pitched for drainage.
A professional can replace a drain pan in 1-2 hours and ensure it's installed correctly so the problem doesn't recur.
You've Cleared the Drain Line But Water Still Leaks
If you've flushed the drain line and it appears clear, but water still pools in the pan or leaks into your home, there's a more complex issue at play. The air handler might not be level, there could be a hidden clog deeper in the line, or the drain line might be undersized for your system's condensate output.
A technician can use a wet/dry vacuum to pull clogs from the outside end of the drain line, inspect the entire drainage path, and verify proper pitch and installation.
The System Is Under Warranty
Most AC manufacturers (Carrier, Lennox, Trane, Rheem, Bryant, Goodman, Amana) require professional installation and service to maintain warranty coverage. If you attempt DIY repairs on a system still under warranty and something goes wrong, you might void that coverage.
If your system is less than 10 years old, check your warranty documentation before attempting repairs. Professional diagnosis and repair protects your warranty and ensures the work is done correctly.
You're Seeing Electrical Issues or Tripped Breakers
If water has leaked onto electrical components, or if your AC is tripping circuit breakers, do not attempt DIY troubleshooting. Water and electricity are a lethal combination. Call a licensed HVAC technician immediately to safely diagnose and repair the system.
Our team at NEXT Heating & Cooling provides heating and cooling services in Metro Detroit with same-day emergency response when safety is a concern. We'll diagnose the root cause, explain your options clearly, and give you a fair price—no pressure, no upselling.
Cost Reality: What AC Leak Repairs Actually Cost in Michigan
Let's talk numbers. Here's what you can expect to pay for common AC water leak repairs in Southeast Michigan, based on current 2026 pricing.
Condensate Drain Line Cleaning: $100-$200
If the only issue is a clogged drain line, a professional cleaning typically costs $100-$200. This includes using a wet/dry vacuum to pull the clog, flushing the line, treating it with algaecide tablets to prevent future growth, and verifying proper drainage.
This is often included as part of a routine AC tune-up, which is why regular maintenance prevents these issues in the first place. Our Next Care Plan includes drain line cleaning during both spring and fall visits for just $5/month.
Drain Pan Replacement: $200-$500
Replacing a cracked or rusted drain pan costs $200-$500 depending on the pan type (metal vs. plastic), accessibility, and labor involved. If the evaporator coil must be lifted to access the pan, labor time increases. Some air handlers have built-in pans that require more extensive disassembly.
Evaporator Coil Replacement: $600-$1,500
If the evaporator coil itself is damaged (from corrosion, refrigerant leaks, or age), replacement costs $600-$1,500 depending on the coil size, refrigerant type, and system configuration. This includes the coil, refrigerant, labor, and system testing.
For systems older than 10-12 years, we often recommend evaluating whether coil replacement makes sense versus replacing the entire system. If you're looking at a $1,200 coil repair on a 12-year-old system, it might make more financial sense to invest in a new, more efficient AC. For context on replacement costs, see our guide on central AC prices in Romeo and Leonard, MI.
Refrigerant Leak Repair and Recharge: $300-$1,200
Refrigerant leak repairs vary widely depending on leak location and severity. A simple leak at a valve connection might cost $300-$500 to repair and recharge. A leak in the evaporator coil or buried in the line set could cost $800-$1,200 or more.
Keep in mind that older systems using R-22 refrigerant (Freon) face much higher refrigerant costs due to the phase-out of R-22 production. Recharging an R-22 system can cost $100-$150 per pound of refrigerant, and a typical recharge requires 3-6 pounds. For R-22 systems with significant leaks, replacement often makes more economic sense than repair.
Air Handler Releveling: $150-$300
If the air handler needs to be releveled to correct drainage issues, expect to pay $150-$300 for labor. This involves physically adjusting the mounting, verifying proper pitch with a level, and ensuring all connections remain secure.
Cost Prevention: Regular maintenance prevents most of these repairs. A $5/month Next Care Plan that includes drain line cleaning, filter checks, and system inspections costs $60/year—far less than a single emergency repair call. Over the life of your system, preventative maintenance saves $1,500-$4,000 in avoided repairs.
Preventing Future AC Water Leaks
Most AC water leaks are preventable with basic maintenance. Here's what actually works, based on 35+ years of keeping Michigan homes comfortable.
Replace Your Air Filter Every 30-60 Days
This is the single most important thing you can do. A clean filter ensures proper airflow, prevents coil freezing, and reduces strain on your entire system. Set a recurring reminder on your phone. Buy filters in bulk (a 12-pack of quality pleated filters costs $60-$80) so you always have one ready.
During peak cooling season (June-August in Michigan), inspect your filter monthly. If you have pets or run the AC constantly, you're on the 30-day replacement schedule.
Schedule Annual AC Tune-Ups Before Cooling Season
A professional AC tune-up in April or May—before the summer heat hits—catches small problems before they become expensive failures. During a tune-up, a technician will clean the condensate drain line, inspect the drain pan, check refrigerant levels, test airflow, and verify all electrical connections.
We see the same pattern every year: homeowners who skip spring maintenance call us in July with emergency breakdowns. The ones who schedule annual tune-ups rarely have emergency issues. It's not a coincidence. For more on the value of seasonal maintenance, read our post on why AC maintenance matters for St. Clair Shores' humid summers.
Flush Your Drain Line With Vinegar Quarterly
Every three months, pour one cup of distilled white vinegar into the condensate drain line access port (the PVC tee fitting near your air handler). Let it sit for 30 minutes, then flush with a cup of water. This prevents algae and mold buildup that leads to clogs.
Do this in March, June, September, and December. It takes five minutes and prevents the majority of drain line clogs.
Keep the Area Around Your Air Handler Clear
Don't store boxes, holiday decorations, or other items directly around your air handler. You need clear access for filter changes and maintenance. Plus, stored items can block return air vents or damage drain lines.
In Michigan basements, we routinely find air handlers buried behind storage. When homeowners can't easily access the unit, they skip filter changes and don't notice problems until water is pooling on the floor.
Consider a Preventative Maintenance Plan
Our Next Care Plan costs $5/month ($60/year) and includes two annual visits—one in spring for AC prep, one in fall for furnace prep. During each visit, we clean your drain line, inspect the drain pan, replace filters if needed, and catch small issues before they become expensive repairs.
Members also get priority scheduling, 10% off all repairs, and no service call fees. Over the life of your HVAC system, this plan typically saves homeowners $1,500-$4,000 in avoided emergency repairs and energy waste.
For more on the financial benefits of maintenance plans, see our breakdown of HVAC maintenance plans in Macomb County.
AC Leaking Water? We'll Diagnose It Honestly.
NEXT Heating & Cooling has been keeping Southeast Michigan homes comfortable for over 35 years. Our NATE-certified technicians will diagnose your AC water leak, explain exactly what's wrong, and give you options without pressure. No upselling. No surprises. Just honest service at a fair price.
Schedule Your Service CallFrequently Asked Questions About AC Water Leaks
Yes, it's completely normal for your AC condensate drain line to drip water outside your home. During humid Michigan summers, your AC can produce 5-20 gallons of condensate per day. If you see water dripping from the outdoor drain line outlet (usually a PVC pipe near your foundation), that means the system is working correctly. However, if you see water leaking inside your home near the air handler or from ceiling vents, that indicates a drainage problem that needs repair.
No, you should turn off your AC immediately if it's leaking water inside your home. Continuing to run the system can cause water damage to your floors, ceilings, and walls. It can also damage electrical components if water reaches them. If the leak is caused by a frozen coil, running the system can damage the compressor—a repair that costs $1,200-$2,500. Turn off the system, clean up the water, and call a licensed HVAC technician to diagnose the problem before running it again.
AC water leak repair costs in Southeast Michigan range from $100-$1,500 depending on the cause. A simple drain line cleaning costs $100-$200. Drain pan replacement runs $200-$500. Refrigerant leak repair and recharge costs $300-$1,200. Evaporator coil replacement costs $600-$1,500. The exact cost depends on the specific problem, parts needed, and labor involved. Most repairs fall in the $150-$400 range for common issues like clogged drain lines or dirty filters.
Intermittent AC water leaks usually indicate a partial drain line clog or a drain pan that's nearly full but not quite overflowing yet. When the AC runs for extended periods during very humid days, condensate production increases and overwhelms the partially blocked drain system. On less humid days or shorter run cycles, the system drains slowly enough that you don't notice a leak. This pattern suggests the drain line needs cleaning before it becomes completely blocked and causes constant leaking.
Yes, absolutely. A dirty air filter restricts airflow across the evaporator coil, causing the coil to run colder than designed. This can lead to ice formation on the coil. When that ice melts—either during defrost cycles or when you turn off the system—it produces more water than the drain pan can handle, causing overflow and leaks. Dirty filters are one of the most common causes of AC water leaks we see in Michigan homes, and it's completely preventable by replacing your filter every 30-60 days during cooling season.
Prevent AC water leaks by replacing your air filter every 30-60 days, flushing your condensate drain line with vinegar quarterly, and scheduling annual professional AC tune-ups before cooling season. During tune-ups, technicians clean the drain line, inspect the drain pan for damage, check refrigerant levels, and verify proper system operation. These three simple maintenance tasks prevent 90% of AC water leaks. A $5/month maintenance plan like our Next Care Plan costs far less than a single emergency repair and keeps your system running reliably for years.
If you see ice on your evaporator coil or refrigerant lines, turn off your AC system immediately at the thermostat and circuit breaker. Let the ice thaw completely—this takes 4-8 hours. Once thawed, replace your air filter with a new one and turn the system back on. If ice returns within 24 hours, you have a more serious problem (likely low refrigerant from a leak, or a blower motor issue) and need professional diagnosis. Never attempt to chip or scrape ice off the coil, as this can damage the delicate aluminum fins.