Recurring gas loss traced to salt-corroded pipe joint at outdoor unit

What we found

Two top-ups in one year with the same problem returning means there is a leak. The seaside exposure made the outdoor pipe joints the first place to inspect.

• Refrigerant pressure was low again, confirming ongoing loss
• Indoor coil and pipe joints showed no signs of leakage
• Outdoor unit flare nut had visible surface corrosion and pitting from salt exposure
• Leak detector fluid applied at the corroded flare nut confirmed active seepage

Salt-laden coastal air had corroded the flare nut at the outdoor unit pipe connection over the years. The corrosion thinned the metal wall enough to allow slow refrigerant seepage. Each top-up restored cooling temporarily, but the leak continued because the corroded fitting was never replaced.

What we did

The compressor is not leaking internally. The corroded flare nut at the outdoor pipe joint needs replacing. Once the new fitting is installed and the joint sealed, the system should hold gas normally. Applying protective coating to exposed outdoor fittings can slow future corrosion in this location.

After the corroded flare nut was replaced and the joint resealed, the system was charged and pressure-tested. Gas pressure held stable. The cycle of repeated top-ups stopped.

What we learned

Why coastal aircon units lose gas at the outdoor pipe joints.

• Salt-laden air accelerates corrosion on exposed metal fittings at the outdoor unit, especially flare nuts and service valve connections.
• The corrosion thins the fitting wall gradually, creating a slow seepage point that is not detectable during a routine top-up visit.
• Replacing the corroded fitting and sealing the joint stops the leak permanently. Repeated top-ups without inspecting the joint just delays the real fix.