Recurring gas loss traced to pinhole leak in concealed pipe run

What we found

We started by pressure-testing the pipe run instead of topping up a third time.

• Nitrogen pressure test showed a slow drop over the concealed section of the pipe run behind the bedroom wall
• Exposed pipe joints at the indoor and outdoor unit were tight — no leak at accessible connections
• Compressor suction and discharge pressures were consistent with low charge, not internal compressor failure

A pinhole had developed in the copper refrigerant pipe inside the wall cavity. Moisture from the concealed environment had corroded a small section of the pipe over the years. The leak was slow enough that gas held for weeks before the charge dropped below the cooling threshold.

What we did

We accessed the affected section of the pipe run and patched the pinhole. The system was then evacuated, recharged, and pressure-tested again to confirm the repair held.

Gas charge has held steady since the repair. The recurring top-up cycle stopped. The compressor was confirmed healthy throughout — no replacement needed.

What we learned

Recurring gas loss — top-up vs. leak repair.

• If gas holds for a few weeks then drops, the leak is slow. Fast leaks empty in days. Slow leaks point to pinhole corrosion in the pipe run, not compressor seals.
• Topping up without pressure-testing the pipe run means the root cause is never found. Each top-up buys time but does not fix the leak.
• Concealed pipes behind walls corrode from moisture exposure over the years. A nitrogen pressure test isolates the concealed section and confirms whether it holds.