Discovering that your air conditioner unit is leaking can feel stressful, especially during a hot day or in the middle of a busy work week. Whether you’re running a commercial system in an office in Bristol or using a domestic unit at home, unexpected leaks are more than just inconvenient they can lead to water damage, system failure, and higher energy bills.
At Controlled Climate, we’ve spent over 25 years working with air conditioning systems across the South West. We’ve seen every kind of leak and fixed them all. In this guide, we’ll explain five of the most common causes of air conditioning leaks, how to spot them early, and most importantly, how to prevent them from returning.
Why Is My Air Conditioner Leaking Water?
Before diving into specific causes, it helps to understand how your AC system is designed to handle moisture. All air conditioning systems remove humidity from the air. This water (condensate) normally drains safely via a condensate pipe. However, if any part of that process is disrupted, such as blocked filters, cracked pipes, or frozen coils, water can overflow and leak from the unit.
Now, let’s explore the five most common reasons behind a leaking air conditioner, starting with the simplest (and most preventable).
1. Blocked Air Filter Restricting Airflow
A clogged air filter is one of the most frequent causes of AC issues, and it’s often the easiest to fix. When a filter becomes dirty or blocked, it restricts airflow over the evaporator coil. This causes the coil to become too cold and may freeze. When the system shuts off or warms up, the ice melts rapidly, leading to pooled water and eventual leaks.
Signs of a Blocked Filter:
- Reduced airflow from the vents
- Strange noises from the indoor unit
- Ice forming on the outside unit or refrigerant lines
- The system is cycling on and off more than usual
How to Prevent It:
- Check your filter monthly, especially during peak summer use
- Replace or clean filters every 1–3 months
- Schedule annual servicing
2. Clogged Condensate Drain Line
The condensate drain line removes excess moisture from your system. Over time, it can clog with mould, algae, or dirt, especially in humid environments. When blocked, water can back up and overflow into your property.
Warning Signs:
- Musty or damp smells
- Pooling water around the air handler
- Your AC is shutting off unexpectedly
- Increased humidity indoors
How to Prevent It:
- Flush the line every 3–6 months with warm water and white vinegar
- Use a wet/dry vacuum to remove minor clogs
- For persistent issues, request a free aircon survey to evaluate your system’s condition
3. Frozen Evaporator Coil
If you see ice on your AC system, a frozen evaporator coil is likely the culprit. When the coil defrosts, excess water may flood the drip pan and leak.
Causes Include:
- Dirty or neglected air filters
- Faulty or slow-running fans
- Refrigerant leaks
- Blocked air vents or ductwork
How to Prevent It:
- Replace filters and clean vents regularly
- Ensure fan motors work efficiently
- Schedule refrigerant checks yearly
- Turn off the unit and run the fan to defrost coils
If your system keeps freezing, contact our engineers for professional support.
4. Cracked or Rusted Drain Pan and Pipes
The drain pan collects moisture from the evaporator coil. Over time, especially in older systems, it can rust, crack, or degrade, causing leaks even when everything else works properly.
What to Look For:
- Cracks or rust in the drain pan
- Water stains under the unit
- Persistent leaks despite filter or drain line maintenance
How to Prevent It:
- Inspect the drain pan during annual servicing
- Replace aged pans or corroded parts
- Look for signs of rust at joints and pipe connections
For larger-scale needs, explore our commercial air conditioning installation services.
5. Outdoor Temperatures and Seasonal Changes
Fluctuating temperatures in spring or autumn can impact how your system drains moisture. When the air is too cool, condensation doesn’t evaporate properly, leading to leaks.
Why It Happens:
- Cooler weather slows down evaporation
- Moisture builds inside the unit
- Running the AC in low outdoor temperatures (under 15°C) can unbalance the system
How to Prevent It:
- Use breathable covers to protect outdoor units during winter
- Avoid running AC during cold weather
- Learn more about choosing the right AC system for the UK climate
Common Follow-Up Question: Do I Need to Replace the Unit?
Not always. Most AC leaks are fixable. However, consider replacement if your unit is:
- Over 10–12 years old
- Frequently leaking despite servicing
- Increasing energy bills
- Using outdated refrigerants
We can recommend and install modern, energy-efficient systems built to reduce long-term issues.
FAQs About Leaking Air Conditioning Units
Is a leaking air conditioner dangerous? Yes, especially if moisture reaches the electrics or causes mould. Always inspect leaks promptly.
How much does it cost to fix an AC leak? It varies. Basic clogs might cost under £100. More serious repairs or refrigerant issues are more complex.
Can I fix a leak myself? You can clear drain lines and clean filters. But never touch refrigerants, it’s illegal without F-Gas certification.
Is it safe to use my AC if it’s leaking? No. Shut it off and contact a professional. Using a leaking system could worsen the damage.
Serving Bristol and the South West
From domestic systems in Clifton to commercial units in Weston-super-Mare, we support homes and businesses across:
- Bristol
- Bath
- Weston-super-Mare
- Portishead
- Yate
- Surrounding areas within a 60-mile radius
With over 25 years of experience, our team provides reliable servicing, diagnostics, repairs, and installations tailored to the needs of your property.
Final Thoughts: Don’t Ignore That Leak
A leaking air conditioner might seem minor, but early action makes all the difference. Whether it’s a frozen coil or a blocked pipe, we’ll help you get back to cool, efficient comfort.
Book Your Inspection Today
Noticed a leak? Book an inspection, and our engineers will identify the cause, repair any damage, and guide you on preventing future leaks.