Two Top-ups In Four Months: Slow Leak At The Indoor Pipe Joint

• •Concern: Worry was about being stuck in a cycle of repeated top-ups with no end in sight
• •Key check: Nitrogen pressure test held overnight to confirm pressure drop

The unit was blowing warm air on arrival. Gauge pressure was well below normal operating range, consistent with the two previous top-ups fading. Low gas was confirmed, but that only describes the symptom. The key question was where the refrigerant was going. We connected a nitrogen charge to the system, sealed all service ports, and left the test running overnight to measure whether pressure held or dropped.

• •Refrigerant pressure well below operating range. Confirmed low gas.
• •Applied nitrogen charge and sealed the system for an overnight hold test.
• •Pressure had dropped measurably by the next morning. Active leak confirmed.
• •Leak traced to the indoor flare joint using bubble solution. Small gap at the connection.

The flare joint at the indoor unit connection had developed a slight gap where the copper flare meets the brass fitting. Over years of thermal cycling, the pipe expanding when the compressor runs and contracting when it stops, the flare had deformed just enough to lose its seal. The gap was too small to detect without bubble solution, but large enough for refrigerant molecules to escape steadily. The loss rate was slow, taking weeks to drain below the cooling threshold, which is why each top-up appeared to work before the same pattern returned.

The joint was fixable without replacing any parts. We removed the old flare, cut back the copper pipe to clean metal, and formed a fresh flare using a calibrated tool to ensure the correct cone angle. The joint was reconnected, torqued to spec, and sealed. We ran a second overnight nitrogen test to confirm the new connection held pressure. Once the hold was verified, the system was evacuated and recharged to the manufacturer-specified gas weight. No compressor or coil work was needed.

The joint was sealed and the system recharged. Cooling has been stable since the repair. No further top-ups have been needed.

Top-up and hold vs top-up and repeat.

• •A top-up that holds for years usually means the original charge was slightly low or a hairline gap sealed itself under pressure. No further action needed.
• •A top-up that fades in weeks means gas is actively escaping through a physical gap. Each refill leaks out through the same opening because nothing has changed structurally.
• •A nitrogen pressure test is the only way to confirm whether the system holds or bleeds. Without it, every top-up is a guess, and guessing compounds the cost.
• •Ask your technician whether they pressure-tested before recharging. If they only checked gauge pressure with refrigerant in the system, they confirmed low gas but not whether there is a leak.