Two top-ups in four months: slow leak at the 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 | Reviewed 3 Mar 2026
Case summary
Daikin Wall-mounted8 years oldHDBClementi, Singapore
- Concern
- The owner worried about 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.
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 previous technician kept repeating the top-up without looking for 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.
Related reading
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