Aircon Refrigerant Leak vs Low Gas

Case Details

What We Checked

• Refrigerant pressure well below normal range.
• Nitrogen pressure test applied — system pressurised and gauges left overnight.
• Pressure dropped by next morning, confirming an active leak.
• Leak located at indoor-side pipe connection using bubble solution.

The Diagnosis

The flare connection at the indoor-side pipe joint had a small gap caused by a flare nut that was not torqued to specification during the original installation. Over time, thermal cycling — the pipe expanding when warm and contracting when cold — gradually worked the already undertightened joint loose enough for refrigerant molecules to escape through the gap. The leak rate was slow: not enough to cause a noticeable pressure drop in a single day, but sufficient to drain the system charge over three to four weeks. Each gas top-up restored the correct charge level temporarily, but because the joint was never inspected or retightened, the refrigerant escaped through the same path every time. The compressor, evaporator, and condenser were all undamaged.

What Fixed It

We retightened the flare nut at the indoor-side connection to the correct torque specification, then applied bubble solution to confirm no further leakage at the joint. The system was evacuated with a vacuum pump to remove any moisture that may have entered through the leak, then recharged with the manufacturer's specified refrigerant weight. We ran a full cooling cycle and measured the temperature differential across the indoor coil to confirm the charge level was correct. The connection should now hold indefinitely.

The connection was repaired and the system recharged. Cooling has been stable since, with no further top-ups needed.

Why This Happens

How to tell if it's low gas vs. a leak.

• A one-time top-up that holds for years usually means the system was undercharged at installation or lost a small amount during a past service. There is no active leak — the charge just needed correcting once.
• Repeated top-ups every few weeks or months means there is an active leak somewhere in the circuit. Topping up without finding the leak is treating the symptom while the cause continues draining your refrigerant and your money.
• A nitrogen pressure test left overnight is the standard method for confirming an active leak. The system is pressurised with dry nitrogen and the gauges are monitored. Any pressure drop over the test period confirms gas is escaping. Bubble solution then pinpoints the exact location.
• Most slow leaks in residential systems occur at pipe joints — flare connections, brazing points, or Schrader valve cores. These are accessible and repairable without replacing any major components.