Two Top-Ups in Four Months: Slow Leak at Indoor Pipe Joint

Two top-ups in four months, with more refills starting to look normal. When repeated topping up stops being maintenance.

By Team Snowflake | Updated 24 Aug 2026

Teaching case based on recurring Snowflake service patterns; identifying details are combined.

How this presents

Two top-ups inside four months, each buying a few weeks of proper cooling before the fade returns. The interval between refills is the diagnostic fact, and it had not been recorded or acted on either time.

Setup: Daikin Wall-mounted10-12 yearsHDBClementi
Misread as: Routine topping up, until three or four refills a year start to look normal.
Check first: An overnight pressure hold test, before any more gas goes in

Outdoor condenser unit connected to manifold gauges for gas pressure testing — Gauges left connected on a sealed system. A reading taken once says the charge is low; a reading left overnight says whether the circuit holds it.

What else produces this

A low pressure reading confirms the symptom and settles nothing: it is equally true of a leak and of an undercharge. What separates them is time. A sealed circuit charged to test pressure and left overnight holds; a leaking one does not. That test costs a return visit and removes the guesswork a third top-up would preserve.

A low pressure reading confirms the system is short. It does not say whether the gas leaked out or was never fully charged.
Test pressure applied with every service port sealed turns the question into an overnight one.
A reading that has dropped measurably by morning proves an active leak rather than a one-off undercharge.
Bubble solution then narrows it to a single point: a fine gap where the copper pipe meets its brass fitting indoors.

Why it happens

The joint loosens by working, not by failing. Copper expands as the unit runs and contracts when it stops, and a joint cycles through that movement every day for years. Eventually the seal gives up a gap too fine to see and wide enough to pass refrigerant slowly. The loss is gradual, which is what makes it convincing as a charge problem: cooling stays acceptable for weeks after each refill before dropping below usable.

What resolution involves

The joint is remade rather than replaced. It comes off, the copper is cut back to clean metal, and a fresh joint is formed and reconnected. What makes that a repair rather than a hope is the second hold test: pressure goes back in and sits overnight again before any refrigerant does. Only once it holds is the system cleared and recharged. No compressor or coil work is involved at any point.

How to tell it worked

The proof is the order of operations. A repair holds test pressure overnight before any gas goes in; a recharge that happens first is a top-up with a repair's invoice attached. Ask which came first.

Before you approve a quote

Refrigerant is not consumed, so a system that runs short is losing it

If cooling fades weeks after a refill, the gas is escaping and the escape point needs naming.
Repeated top-ups treat the symptom. Each one costs money and buys the same few weeks as the last.
An overnight hold test answers whether the circuit is sealed, and it should run after the repair and before the recharge.

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. The pattern is consistent: cooling for a few weeks after each refill, then the same fade. 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 its pressure overnight. A leaking one gives some of it up. A reading that has fallen measurably by morning proves an active leak, and justifies going further with bubble solution at the joints.

Where do refrigerant leaks form on wall-mounted aircons?

Joints move, so joints leak. A common one sits at the indoor pipe joint where copper meets a brass fitting. The pipe expands while the unit runs and contracts when it stops, and years of that movement can work the seal loose. The gap is usually too fine to see, and bubble solution makes it visible at once.

Leaking pipe joint: repair it or replace the aircon?

Repair, when the leak is a single located point. The old joint comes off, the copper is cut back to clean metal and a fresh joint is formed. Another overnight test confirms it holds before the system is cleared and recharged. No compressor or coil work enters it, and the repeat top-up cycle ends.

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