Air conditioners near the bay: protecting outdoor units from salt air

Hobsons Bay has more than 20 kilometres of bay frontage. Altona, Seaholme and Williamstown sit right on it, Seabrook is close behind, and Port Melbourne faces the same water to the east. Onshore breezes carry fine salt spray inland, and it settles on anything left outside, including the outdoor half of every split and ducted system.

An outdoor unit is built to pull large volumes of air across its coil, so it collects more salt than most things in the yard. Salt draws moisture out of the air and keeps surfaces damp. On most coils that means the thin aluminium fins and the copper tubes they're bonded to corrode where the two metals meet. Fins go powdery and start to flake, the coil moves heat less effectively, and eventually a tube or joint can begin to leak.

The rest of the unit isn't spared. Cabinet screws, panels and wall brackets rust, the fan motor's bearings wear, and the isolating switch beside the unit and the terminals inside it can corrode. Electrical corrosion is the kind you don't see until something stops working.

Distance and exposure both count. BlueScope's marine-environment guide, based on AS 4312 and described as a guide only, classes Port Phillip Bay from Altona to Portsea beaches as an exposed marine environment and Williamstown as calm marine. An industry summary of AS 4312 from the Galvanizers Association puts land within 50 m of a sheltered bay's shoreline in a harsher corrosivity category than land from 50 m to 1 km inland, and gives Port Phillip Bay as its example.

In practice, a house on the Esplanade in Altona or a street near Williamstown Beach asks far more of an outdoor unit than one a few streets back, and a unit facing straight onto the water ages faster than one tucked behind the house. Further inland the effect fades, but homes a kilometre or so from the shore can still see salt on outdoor equipment after a run of windy days.

Where there's a choice, put the outdoor unit on the side of the house away from the bay and out of the prevailing wind. A wall or fence between the unit and the water takes the worst of the spray. That shelter can't come at the expense of airflow, though: a unit boxed into a corner breathes its own exhaust and loses capacity on hot days, so it still needs the clearances in its installation manual.

Units sheltered from rain don't get rinsed by it, so salt builds up on them faster than on surfaces out in the open. That's not a reason to leave a unit fully exposed, but it does mean a tucked-away unit under deep eaves needs its coil looked at more often.

Mount the unit off the ground on a sound base or bracket so it isn't sitting in damp leaves, and keep garden beds, mulch and sprinklers away from it.

Many manufacturers make coastal or anti-corrosion versions of their outdoor units, with a protective coating on the coil fins and better-protected cabinet parts. Some also set conditions in their installation instructions for units close to salt water. Read the manual for the model you're considering, or ask your installer to, before it's ordered, not after it's on the wall.

Protective coatings can also be applied to a standard coil, ideally when the unit is new and clean. A coating slows corrosion; it doesn't stop it, and it doesn't replace regular cleaning.

Small parts matter as much as the coil. Ask for brackets, bolts and screws suited to a coastal site, and a weatherproof isolator mounted where it isn't catching direct spray. A rusted bracket bolt can fail long before the unit does.

Your part is simple. Keep leaves and clippings clear of the unit and look at it every few months. White crust on the fins, rust streaks from screws or brackets, and flaking or crumbling fins are all reasons to book a service. Don't hose it, spray cleaners into it or throw a cover over it while it can run. The fins bend easily and the electrical parts aren't made for a jet of water.

At a service near the bay, the outdoor coil should be cleaned and checked for corrosion, along with fixings, brackets, the isolator and electrical connections. Federal bench tests found common faults in air conditioning equipment caused average energy losses of 14% to 20% in most tests, and a salt-clogged coil is one of the more common faults close to the water. If the unit runs a lot, a yearly service is a reasonable rhythm for beachside homes.

Evaporative coolers on bayside roofs face the same air. Their cabinets and metal parts corrode sooner near the water, so give them the same attention at their spring service.

Refrigerant runs in a sealed loop and isn't used up. A system near the bay that slowly loses cooling and heating over a couple of seasons, or ices up on its pipes, may have a corroded coil or joint that has started to leak. The Australian Refrigeration Council says no one may top up a system until it has been fully tested and every identified leak repaired, and the work needs a licensed technician.

Whether to repair depends on where the leak is and how the rest of the unit looks. A leaking joint on a sound coil can be repaired. A coil that's corroded all over will keep finding new places to leak, and on an older unit replacement is usually the sensible call.

If you do replace, choose with the site in mind: a coastal-spec unit, corrosion-resistant fixings and a better position if the old one copped the worst of the wind. Any new circuit or isolator is electrical installation work, and Energy Safe Victoria lists air conditioning as non-prescribed work, so the electrician completes a Certificate of Electrical Safety and gives you a copy within 30 days.