Hey again—it’s Samantha! 💁
So, picture this: You walk into your utility room and squish—your sock is soaked. There’s a weird musty smell in the air, your AC’s running nonstop, and your house still feels like a swamp. 😩
Yep, I’ve been there. And if you’re reading this, there’s a good chance your evaporator coil might be leaking.
When it happened to me, I didn’t even know what an evaporator coil was—let alone why it would leak. But now? I could give a TED Talk. So buckle up, because I’m going to walk you through what causes evaporator coil leaks, how to spot the warning signs, and what your next smart steps should be.
Spoiler: it’s fixable. You’ve got this. 👏
What Is an Evaporator Coil (and Why Is It Leaking)?
Your evaporator coil is the part of your air conditioning system that absorbs heat from the air in your home. It lives inside your air handler or furnace cabinet, and refrigerant flows through it like a sponge soaking up heat.
When this coil develops tiny pinhole leaks, that refrigerant escapes—and your AC loses its cooling mojo.
So why does this happen? Let’s break it down.
The Top 5 Reasons Evaporator Coils Leak
1. Formicary Corrosion (a.k.a. the silent destroyer) 🧪
This is the #1 cause of evaporator coil leaks—and you’ve probably never even heard of it.
Formicary corrosion is caused by indoor air pollutants like formaldehyde (yep, that stuff from furniture glue, paint, and cleaning products). These chemicals mix with moisture in your home and create organic acids that slowly eat away at copper tubing.
The result? Microscopic pinholes in your coil.
According to Goodway, this corrosion doesn’t happen overnight—it builds up over years, and by the time you notice a leak, it’s already spread like rust under a car hood.
2. Dirty Air Filters and Poor Airflow 🌬️
When your air filter gets clogged, airflow over the coil drops. That can cause excess condensation to form, which increases moisture and contributes to corrosion over time.
Also, moisture + pollutants = corrosion cocktail. 🍸 Not fun.
3. Improper Installation 🔧
Coils that aren’t installed level or aren’t properly sealed can trap moisture, which leads to—you guessed it—corrosion.
Some installers don’t use proper pan slope, or forget to clean the lines before brazing. It sounds small, but it can lead to huge problems down the road.
4. Wear and Tear from Vibration 🛠️
Your HVAC system vibrates every time it turns on. If your coil isn’t secured properly, those vibrations can slowly weaken joints and connections, eventually leading to leaks.
It’s kind of like bending a paperclip over and over until it snaps.
5. Low Refrigerant and Freezing/Thawing ❄️🔥
If your system has already been leaking and running low on refrigerant, the coil can freeze. Then when it thaws, it expands and contracts—putting stress on already-weak spots in the copper.
Over time, that stress can cause small cracks.
And yep—leak city. 🏙️
How to Tell If Your Evaporator Coil Is Leaking
Here are some telltale signs to look for (trust me, I’ve lived them all):
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Your AC runs nonstop but doesn’t cool well.
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There’s water pooling near your furnace or air handler.
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You hear hissing sounds from the coil area.
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Your energy bill suddenly jumps.
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There’s a musty, moldy smell around your vents.
If you’re seeing any of these signs, it’s time to check the coil.
And yes—you can sometimes spot leaks yourself, especially with a flashlight and some soap solution. But most of the time, they’re microscopic and require pro tools like an electronic leak detector or UV dye test.
This article from John C. Flood is a great beginner-friendly overview if you want to go full Sherlock Holmes. 🕵️
Is It Safe to Run Your AC with a Leaky Coil?
Short answer: Nope.
Longer answer: You can, but you really shouldn’t.
Here’s why:
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You’ll waste refrigerant (and money).
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Your compressor could overheat and fail.
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It could create moisture buildup and mold.
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The system could freeze and do even more damage.
If you keep topping off refrigerant without fixing the leak, you’re basically putting duct tape on a leaky tire.
And by the way, adding refrigerant over and over is illegal in many states unless the leak is fixed. Here’s the EPA’s rulebook if you want to be extra informed.
Can You Repair a Leaky Coil? Or Do You Need to Replace It?
Ah, the million-dollar question. 💸
Here’s my personal take—based on lots of research, a few HVAC tech visits, and one very expensive lesson:
You can try to repair a coil leak if:
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It’s just one small, accessible leak.
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Your coil is fairly new and still under warranty.
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You’re not planning to keep the system long-term.
Most techs will use a soldering or brazing technique to seal the leak. In some cases, they may use a sealant product like A/C EasySeal—but those are a temporary fix at best.
HVAC Know It All has a helpful article on when sealants are appropriate and when they’re not.
But… you should replace the coil if:
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There are multiple leaks or widespread corrosion.
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Your system is more than 7–10 years old.
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It uses outdated refrigerants like R-22.
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The repair cost is more than 30–40% of a new coil.
Trust me, I tried to go the patch route once—and the new leaks showed up faster than I could say “Freon.” 🥴
How Much Does Coil Replacement Cost?
On average, expect to pay $600 to $2,000, depending on:
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The brand and model
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Whether it’s cased or uncased
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Your local labor rates
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Whether refrigerant and flushing are included
Need more help comparing? Angi has a solid guide that breaks it down by system type and coil design.
If you're ready to shop, I highly recommend checking out
👉 The Furnace Outlet’s evaporator coil collection.
They’ve got vertical, horizontal, A-coils, slab coils—whatever fits your setup. Their customer service is also super helpful if you’re unsure what matches your system.
How Much Does Coil Replacement Cost?
On average, expect to pay $600 to $2,000, depending on:
-
The brand and model
-
Whether it’s cased or uncased
-
Your local labor rates
-
Whether refrigerant and flushing are included
Need more help comparing? Angi has a solid guide that breaks it down by system type and coil design.
If you're ready to shop, I highly recommend checking out
👉 The Furnace Outlet’s evaporator coil collection.
They’ve got vertical, horizontal, A-coils, slab coils—whatever fits your setup. Their customer service is also super helpful if you’re unsure what matches your system.
How to Prevent Coil Leaks in the Future
Let’s be real—coil leaks are a pain. So here’s what I do now to prevent them:
1. Change your air filters regularly.
Every 1–3 months depending on your system and how many pets you have.
2. Keep your coil clean.
Use foaming no-rinse coil cleaner at least once a year.
3. Reduce indoor pollutants.
Avoid heavy use of chemical cleaners and choose low-VOC paints and furniture.
4. Get annual HVAC maintenance.
A tune-up can catch early signs of corrosion and other wear.
5. Install a whole-home air purifier.
It helps remove corrosive gases that contribute to formicary corrosion.
Final Thoughts from Samantha 💁🔍
Leaks may start small—but left unchecked, they can ruin your whole cooling system and leave you hot, frustrated, and financially frazzled.
But now? You know what to look for. You know what causes the leaks. And you know when to call in the pros versus when to simply order the right part.
If it’s time for a fresh start, or if your tech recommends replacement, head over to
👉 The Furnace Outlet’s evaporator coils
They’ve got top-tier brands, great prices, and the support you need to match the right coil to your setup—without playing guessing games.
Deciding between vertical or horizontal coils? Visit: What’s Right for Your HVAC Setup?
You’re smarter than the average homeowner. And now? You’re basically a leak detective. 🕵️💦
Stay cool, stay proactive—and never settle for a soggy sock moment again.
— Samantha, Home Advisor
