Two top-ups in four months: slow leak at indoor pipe joint

The bedroom aircon cooled well for a few weeks after each top-up, then faded again. Two top-ups in four months pointed to a leak, not a fault that a third top-up would fix. The question was where the gas was going.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Daikin Wall-mounted8 years oldHDBClementi, Singapore

Concern: The prospect was being stuck paying for top-up after top-up, with no end to the cycle.
Found: Slow refrigerant leak at indoor pipe joint
Key check: pressure hold test held overnight to confirm pressure drop
Result: With the joint sealed and the system recharged, cooling has held steady since the repair. No further top-ups have been needed, and the top-up cycle is over.

Outdoor condenser unit connected to manifold gauges for gas pressure testing

What we were told

The unit had been topped up twice in about four months. Each time, cooling returned for a few weeks, then faded again. The top-up kept being repeated with no attempt to find why the gas was running out.

What we checked

The unit was blowing warm air on arrival. Gas pressure read low, which matched the fading after each earlier top-up. Low gas confirmed the symptom, but a third top-up would only repeat the cycle. We needed to find where the gas was escaping. So we charged the system with test pressure, sealed every service port, and left it overnight to see whether the pressure held or fell.

Gas pressure read low, confirming the system was short on refrigerant.
We applied test pressure and sealed the system for an overnight hold test.
By the next morning, the pressure had dropped measurably. That proved an active leak, not a one-off undercharge.
Bubble solution at the joints found the leak at the indoor pipe joint, a small gap at the connection.

What we found

A small gap had opened at the indoor pipe joint, where the copper pipe meets the brass fitting. The pipe expands as the unit runs and contracts when it stops, and over the years that movement worked the joint loose enough to lose its seal. The gap was too fine to see without bubble solution, but wide enough to let gas leak out slowly. The loss took weeks to drag cooling below a usable level, so each top-up seemed to work before the same pattern came back.

What fixed it

The joint could be fixed without replacing any major part. We removed the old joint, cut the copper pipe back to clean metal, and formed a fresh joint for a proper seal. We reconnected it and ran another overnight pressure test to confirm it held. Once it passed, we cleared the system and recharged it to the correct level. No compressor or coil work was needed.

Outcome

With the joint sealed and the system recharged, cooling has held steady since the repair. No further top-ups have been needed, and the top-up cycle is over.

What this case teaches us

A top-up that fades again means the gas is leaking out

Refrigerant does not get used up. If cooling fades weeks after a top-up, the gas is escaping somewhere and the leak needs finding.
Repeated top-ups treat the symptom, not the cause. Each one costs money and buys only a few more weeks.
An overnight pressure hold test shows whether the system holds gas or loses it. That answer decides whether a top-up is worth doing at all.

Questions this case answers

Aircon needs topping up twice in a few months: is that normal?

No. Refrigerant is not used up the way fuel is, so a system that keeps running short is losing it somewhere. In this Clementi bedroom the pattern was consistent: cooling for a few weeks after each refill, then fading again. That repetition is the signal to stop refilling and start looking for the escape point.

What is an overnight pressure hold test?

Test pressure is put into the system, every service port is sealed, and the reading is left to sit. A sealed circuit holds; a leaking one drops. The pressure on this unit had fallen measurably by morning, which proved an active leak rather than a one-off undercharge and justified going further with bubble solution at the joints.

Where do refrigerant leaks form on wall-mounted aircons?

Joints move, so joints leak. The one found here was at the indoor pipe joint where copper meets a brass fitting. The pipe expands while the unit runs and contracts when it stops, and over the years that movement can work the seal loose. The gap was too fine to see, and bubble solution made it visible at once.

Leaking pipe joint: repair it or replace the aircon?

Not when it is a single located point. The old joint was removed, the copper was cut back to clean metal and a fresh joint was formed, then another overnight pressure test confirmed it held before the system was cleared and recharged. No compressor or coil work came into it, and the repeat top-up cycle stopped.

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