Gas topped up three times: hidden leak at the service valve
Cooling can keep fading after several gas top-ups when the leak is small and sits where routine checks skip. This unit lost gas three times in a year. The source turned out to be the valve core at the service port.
By Team Snowflake | Reviewed 26 Feb 2026
Case summary
Midea Wall-mounted9 years oldHDBYishun, Singapore
- Concern
- The worry was a serious leak in the indoor coil or compressor that would need an expensive part.
- Found
- Hidden leak at the service valve core
- Key check
- Focused leak checks around the service port and valve core after the wider circuit looked stable
- Result
- After the valve-core replacement and pressure recheck, cooling held steady and the repeat top-up cycle stopped.
What we were told
After each gas top-up the unit cooled well for a while, then faded again. This had happened three times, with no clear answer for where the gas was going.
What we checked
When cooling fades on the same schedule after every top-up, the job shifts from adding gas to finding the leak. We reviewed the top-up history to gauge how fast the gas was escaping. We then worked along the refrigerant circuit in order, from the main pipe joints down to the smaller service-port points that a standard leak check often skips.
Three top-ups in under a year, with cooling fading each time. That fit a slow, steady leak rather than a sudden failure.
Checks on the main pipe joints, the pipe fittings, and the indoor coil connections found no leak.
A bubble test and an electronic sniffer both picked up a leak at the service-port valve core on the outdoor unit.
The leak was small but steady, enough to drain system pressure over two to three months.
The valve core was worn and slightly deformed from age and from being opened on each past top-up.
What we found
The valve core inside the outdoor service port had worn and slightly deformed over years of use. Each time a technician connected gauges for a top-up, the core was pressed open and released. Over nine years and several top-ups, its sealing surface wore down just enough to let gas slip past. The leak was too small to find without focused testing at the port itself, which is why wider circuit checks on earlier visits had cleared the system. Gas escaped slowly through the worn seal, draining enough pressure over two to three months to cause clear cooling loss. Each top-up restored pressure and cooling, but the leak stayed open. That is the cycle that kept repeating.
What fixed it
We explained that the leak was at the valve core, a small replaceable part inside the service connection, not at the indoor coil or compressor. We fitted a matched new core, then ran a pressure hold test before recharging. The pressure held steady with no drop, which confirmed the leak was sealed. We recharged the system and checked that cooling was back to normal. No other circuit repairs were needed.
Outcome
After the valve-core replacement and pressure recheck, cooling held steady and the repeat top-up cycle stopped.
What this case teaches us
Repeat top-ups point to an unfound leak
- If cooling fades again a few months after every top-up, the gas is escaping somewhere. A top-up only resets the clock.
- The leak can hide at the same connection a technician opens to add gas. Wear there is easy to miss in a wider check.
- Before paying for more gas, ask where the leak was traced. A sealed system holds pressure on a hold test before recharge.
Related reading
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