Gas Keeps Running Out: Pinhole Leak In Pipe Behind The Wall

• •Concern: Risk appeared to be internal compressor failure leaking gas, which would mean a full system replacement.
• •Key check: Performed nitrogen pressure test on the pipe run to confirm a leak in the concealed section, rather than just topping up gas

Rather than topping up a third time, we started by pressure-testing the pipe run to determine whether gas was actually escaping. We connected a nitrogen charge to the system and monitored pressure over four hours. We also checked the accessible joints at both the indoor and outdoor units with bubble solution, and measured compressor suction and discharge pressures to assess whether the compressor itself could be leaking internally.

• •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. The pipe run passes through approximately three metres of concealed space between the indoor unit and the external wall penetration. Over eight years, moisture condensing on the cold copper surface from the surrounding wall environment had corroded a small section of the pipe from the outside in. The resulting pinhole was large enough to let refrigerant escape at a slow, steady rate of a few grams per day, but too small to detect without pressurising the concealed section directly. The loss rate matched the pattern the client described: cooling held for several weeks after each top-up before fading below the threshold.

We opened a small section of the bedroom wall to access the corroded pipe area. The pinhole was visible under magnification, a single point of external corrosion that had eaten through the copper wall. We cleaned the area, applied a brazed patch to seal the opening, and pressure-tested the repaired section with nitrogen to confirm it held. The system was then fully evacuated to remove any moisture or air that had entered through the leak, and recharged to the manufacturer-specified gas weight. We recommended monitoring gas pressure at the next service interval to confirm the repair held long-term.

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

Recurring gas loss: top-up vs leak repair.

• •The fade timeline tells you the leak rate. Gas that holds for a few weeks then drops points to a slow, steady loss, typically a pinhole or hairline crack. Fast leaks empty a system in days and produce obvious symptoms. Slow leaks mimic normal aging, which is why they get dismissed with another top-up.
• •Topping up without pressure-testing the pipe run means the root cause is never found. Each top-up buys a few weeks of cooling but the same gap lets gas out at the same rate. The cycle becomes predictable, and expensive.
• •Concealed pipes behind walls are exposed to moisture in the wall cavity over years. In older condos where the pipe run passes through concrete or brick, condensation on the cold pipe surface accelerates copper corrosion from the outside in. A nitrogen pressure test isolates the concealed section and confirms whether it holds.
• •Ask your technician whether they tested the concealed pipe section separately from the accessible joints. If the indoor and outdoor connections test tight but pressure still drops, the leak is in the wall, and a top-up will not fix it.