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 | Updated 28 Jul 2026

Case summary

LG Wall-mounted4 years oldHDBBukit Batok, Singapore

Concern: The expectation was a failed compressor and a whole system needing replacement.
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 owner still had no explanation for why the gas kept draining away.

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 CH38, a low refrigerant 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.

Questions this case answers

Aircon needs topping up every few weeks: is the compressor failing?

That symptom points at the refrigerant path, not at the compressor. In this Bukit Batok flat the gas pressure was low and matched the reported loss, the indoor pipe joints were dry, and both outdoor pipe joints carried visible corrosion. A bubble test on those joints showed active bubbling.

Why do outdoor pipe joints corrode so fast here?

Sun, rain and constant humidity work on the connection surfaces, and on some outdoor units the joint layout tends to hold water, which speeds it up. Corrosion eats into the seals and leaves small gaps for refrigerant to escape through. That is why a top-up on this unit only ever lasted weeks.

What are the options once a leak is found at the outdoor connections?

Three, and each was laid out with its trade-offs. Weld the leaking joints and recharge, which is cheapest but leaves corroded pipe nearby. Fit a compatible new outdoor unit, which clears the corroded joints and keeps the indoor units. Or replace the full system, which suits a set whose indoor units are also wearing out.

Is welding a corroded joint a permanent fix?

Only where the corrosion is confined to that one spot. If it has spread along the pipe, sealing one gap invites the next one nearby, and we have seen that play out. Ask whether the corrosion is local or runs along the connection, because that answer decides between a weld and a unit change.

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Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.

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