LG unit topped up twice: corroded outdoor pipe connections
Cooling faded a few weeks after every gas top-up, so the owner feared the compressor had failed. The cause was simpler and cheaper to confirm. Refrigerant was escaping through corroded pipe joints on the outdoor unit.
By Team Snowflake | Reviewed 19 Mar 2026
Case summary
LG Wall-mounted4 years oldHDBBukit Batok, Singapore
- Concern
- The owner worried the compressor had failed and the whole system needed replacing
- Previous advice
- Previous contractor topped up gas twice without checking for leaks
- Found
- Refrigerant leak at corroded outdoor unit pipe connections
- Key check
- Bubble test at outdoor unit connections showed active bubbling at both liquid and gas line joints
- Result
- The full system was replaced. We installed new indoor and outdoor units, pressure-tested the piping for leaks, and set the refrigerant charge correctly. Cooling has stayed steady since, with no further gas loss.
What we were told
The unit had been topped up twice in the last few months. Each time, cooling came back for a few weeks, then faded again. The previous contractor said the gas was running low but never explained why it kept dropping.
What we checked
Gas that runs low again so soon after a top-up almost always means an active leak. A sealed system does not lose refrigerant on its own. So we set out to find where it was escaping before talking about any repair, and worked from the indoor joints outward.
Gas pressure was low, matching the reported loss.
The indoor pipe joints were dry, with no sign of leakage there.
Both pipe joints on the outdoor unit showed visible corrosion and green oxidation.
A bubble test on those joints showed active bubbling, confirming refrigerant was leaking out.
The condenser coil was heavily clogged with dust and debris, in line with the unit's age and weather exposure.
What we found
The pipe joints on the LG outdoor unit had corroded over four years of sun and rain. The corrosion ate into the seals and left small gaps where refrigerant slowly escaped. That is why each top-up lasted only a few weeks before cooling faded again. On some LG outdoor units the joint layout tends to trap water, which speeds the corrosion up. The unit had also logged LG error code CH35, a low-pressure warning that fits a system steadily losing gas.
What fixed it
We laid out three options with the trade-offs of each. The cheapest was to weld the leaking joints and recharge the gas. Corrosion had spread along the pipe, though, so new leaks could appear nearby. We have seen that happen before. The second option was a compatible new LG outdoor unit, which fixes the corroded joints fully and resets that unit's lifespan while keeping the indoor units. The third was a full system replacement, which made sense if the aging indoor units were also wearing out. The owner chose the full replacement, weighing the unit's age against the risk of chasing leak after leak.
Outcome
The full system was replaced. We installed new indoor and outdoor units, pressure-tested the piping for leaks, and set the refrigerant charge correctly. Cooling has stayed steady since, with no further gas loss.
What this case teaches us
A gas top-up that keeps fading means find the leak
- If cooling drops again a few weeks after a top-up, the gas is leaking out somewhere. Adding more without finding the source only buys time.
- Outdoor pipe joints corrode after years of sun and rain. They are the first place to check on an older unit, not the compressor.
- Before paying for another top-up or a full replacement, ask where the leak was found and why the proposed fix matches it.
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