Why Does Commercial Air Conditioning Leak Water?
The common causes of a leaking AC system, what to do first, and why it’s a job for an engineer.
Commercial air conditioning leaks water most often because the condensate drain is blocked — but it can also be caused by dirty filters, a frozen evaporator coil, low refrigerant, a cracked or overflowing drain pan, a failed condensate pump, or poor installation. A small amount of water draining away outside is completely normal; water dripping or pooling inside the building is not, and it’s worth dealing with quickly before it damages the building or the system.
In a commercial setting a leak isn’t just a nuisance — water coming through a ceiling can damage stock, equipment, finishes and the floor below, so it pays to understand what’s likely causing it.
First, why does AC produce water at all?
It helps to know that some water is normal. When air conditioning cools a space, moisture in the air condenses on the cold evaporator coil — exactly like droplets forming on a cold drink. That condensation collects in a drain pan and runs away through a condensate drain line (often to outside, or lifted away by a small pump). When everything’s working, you never see it. A leak means that water is escaping somewhere it shouldn’t — so the causes below are nearly all about where the normal water is going wrong.
The common causes
1. A blocked condensate drain line (the usual culprit). Over time the drain line clogs with dust, dirt, algae or sludge. The water has nowhere to go, backs up, and overflows the pan into the building. This is the single most common cause of an AC water leak.
2. Dirty air filters. Clogged filters restrict airflow over the evaporator coil. The coil gets too cold and freezes; when it thaws, the meltwater overwhelms the drain pan and overflows. Dirty filters are one of the most common — and most preventable — causes, which is why filter changes are a staple of planned maintenance.
3. Low refrigerant. A refrigerant shortage (often from a leak elsewhere) drops the pressure in the system and, like a dirty filter, can cause the coil to freeze and then overflow as it melts. Low refrigerant is also an F-Gas matter, so it’s not something to top up and ignore — the leak itself needs finding.
4. A cracked, rusted or misaligned drain pan. The pan that catches the condensate can crack or corrode with age, or sit out of true, so water escapes instead of draining.
5. A failed condensate pump. Where a system can’t drain by gravity, a small pump lifts the water away. If that pump fails, the water simply backs up and overflows.
6. Poor installation. If the drain line was never set at the right gradient, or the unit isn’t level, condensate won’t flow away properly — a fault that shows up as a persistent leak from day one rather than developing over time.
What to do — and why it needs an engineer
The safest first step is to switch the system off. That stops more water escaping and limits damage to the building while you get it looked at.
Beyond that, a leaking commercial system is a job for an F-Gas certified engineer, not something to diagnose or fix from the outside. Most of the common causes — low refrigerant, a frozen coil, a cracked drain pan, an internal blockage, a failed pump — can’t be safely identified or put right without the right training and equipment, and anything involving refrigerant is a legal requirement to handle correctly. Rather than trying to trace it yourself, isolate the unit and get an engineer to find the actual cause. A prompt diagnosis almost always costs far less than the water damage and the breakdown a persistent leak leads to.
Why it’s worth dealing with quickly
In a commercial building a persistent leak does more than make a mess. Standing water and damp lead to mould and damage to ceilings, finishes and anything below; a frozen or low-refrigerant system is working inefficiently and can fail entirely if left; and water near electrics is a genuine hazard. Catching the cause early is almost always cheaper than dealing with the damage and the breakdown together — which is the whole logic behind keeping a commercial system on planned maintenance rather than waiting for it to leak.
If a system is leaking now and you need it sorted, React Cooling runs emergency repair cover across the Midlands, and an F-Gas certified engineer can trace the cause rather than just clear the symptom.
Call our 24hr line: 0330 912 8325 · Book a Site Survey
Related reading
- Why does my air conditioning smell?
- What is HVAC and how does it work?
- What does F-Gas compliance actually require?
- What are the different types of commercial air conditioning system?