Marine Air Conditioning Seawater Leak
Condensate is fresh. If what you have found is salty, it came from the seawater side, and the seawater side runs below the waterline. This is the one fault on this list that can sink a boat, so it is treated accordingly.
Seawater leak: First Checks
Urgent. Find it before you leave the boat.. Taste it or test it. Fresh means condensate and a much calmer page. Salt means keep reading and do not leave the boat until you know where it is coming from.
Where this sits on the seawater loop
- Seacock
- Strainer
- Pump
- Condenser
- Evaporator
- Discharge
- Condensate
Marine air conditioning is water-cooled, and that is what makes it different from a house. The full cutaway is in the guide.
Seawater leak: Diagnostic Steps
Work down it rather than picking the step that sounds most likely. The order is chosen so that the cheap, common causes are eliminated before the expensive, rare ones — which is also the order that stops you paying somebody to clean a strainer.
Shut the air conditioning seacock.
It removes the risk while you look. Everything else on this page is easier with the water off.
Dry everything, then run the unit with the seacock open and watch.
A leak you cannot see is a leak you cannot fix. Drying first makes the source obvious within a minute or two.
Check every hose clamp on the seawater circuit.
Clamps below the waterline should be doubled and in good condition. Single, rusted clamps are the usual finding on an older install.
Inspect the pump seal and the strainer lid gasket.
Pump shaft seals weep as they age, and a strainer lid that has been opened often eventually stops sealing. Both drip rather than gush, which is how they go unnoticed.
Look hard at the skin fitting and seacock themselves.
This is the part that matters. A weeping seacock or a corroded skin fitting is a haul-out job and not one to defer.
When to Stop and Call a Marine Technician
Nothing here is licensed refrigerant work — it is plumbing below the waterline, which is a different kind of serious. If you cannot find and stop it, shut the seacock and get someone aboard.
Handling refrigerant in Australia requires an ARCtick licence under the Ozone Protection and Synthetic Greenhouse Gas Management Regulations, and fixed 240 V work on a vessel is licensed under AS/NZS 3004.2. Both exist for good reasons. Everything above the line is yours; everything below it is not.
Possible Causes of Seawater leak
A loose or corroded hose clamp
Replace in pairs with proper marine-grade clamps.
A weeping seawater pump seal
Rebuild kit or new pump.
A failed strainer lid gasket
New gasket. Keep a spare aboard.
A perished hose
Replace the run. Reinforced marine hose only.
A failing seacock or skin fitting
Haul out. Do not defer this one.
Ranked by how often each one is the answer on Australian boats, not by how often it appears in a service manual. The seawater side dominates this list because our water is warm, our marinas are full of growth, and the strainer is the part nobody opens.
Reporting This Marine Air Conditioning Fault
Tell us the boat, the unit if you know it, and what you found at each step above. We will tell you what we would check next, and whether it is worth a technician's call-out or a new machine. We do not charge for that and we will say if the honest answer is that the unit has had its life.