Aircon Two-Room Cooling Loss, Coil Leak

Case Details

What We Checked

• Operating pressure dropped below expected range.
• Shared bedroom branch showed the earliest cooling decline.
• General flare checks were negative.
• Localized leak evidence appeared at one indoor coil return bend.

The Diagnosis

A pin-hole leak had developed at a return bend on one indoor evaporator coil. Return bends are the tight U-shaped copper sections that connect adjacent coil tubes. Over years of thermal cycling — the coil expanding when warm and contracting when cold — stress concentrates at these bends. Eventually a micro-fracture opens and refrigerant seeps out slowly. Because both bedrooms shared a common refrigerant branch downstream of the leak, every gram lost affected both rooms equally. That is why the living room held up longer — it sat on a separate branch that still had adequate charge.

What Fixed It

We explained two options. The first was a targeted braze repair at the confirmed return bend — this seals the pin-hole and preserves the existing coil. The second was a full coil replacement, which is more thorough but significantly more expensive and requires a longer downtime. Given that the leak was a single isolated point with no corrosion elsewhere on the coil, we recommended the braze repair as the more proportionate response. We also noted that if the repair held through a pressure retest, the system would be fully functional without replacing any major component.

After leak-path correction, cooling stability improved and the repeat top-up cycle was no longer needed.

Why This Happens

Why linked room decline points to a shared refrigerant path.

• When two rooms decline together while a third holds, the leak is almost certainly on the shared branch feeding those two rooms — not a system-wide charge problem. Ask your technician which branch each room sits on before accepting a full-system diagnosis.
• General flare-joint checks are a good starting point, but they miss faults inside the coil itself. Return bends are hidden behind the coil face and need targeted dye or bubble tracing to confirm — ask whether the technician checked coil bends specifically.
• Repeated top-ups without leak confirmation are a warning sign. Each top-up temporarily masks the symptom, but the refrigerant loss continues and the cost accumulates. A single confirmed leak repair is almost always cheaper than three or four top-ups.
• A nine-year-old coil developing a pin-hole at a return bend is not unusual. Thermal cycling stress builds over thousands of cooling cycles and the copper gradually fatigues at the tightest bends. This does not mean the rest of the system is failing.