Gas Topped up Three Times: Hidden Leak at the Service Valve

Gas has gone in three times in a year. A leak that survives several searches is sitting where nobody thought to look.

By Team Snowflake | Updated 24 Aug 2026

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

How this presents

Cooling restored by a refill, holding for two or three months, then fading to the same point. Three times inside a year, with the wider circuit checked each time and nothing found. The consistency of the interval is what makes it a leak rather than an accident.

Setup: Midea Wall-mounted10-12 yearsHDBYishun
Misread as: Indoor coil or compressor failure, the expensive end of a repeat top-up.
Check first: The service port itself, once the wider circuit reads clear

R410a refrigerant canister connected to manifold gauges during system recharge — A top-up rig on the balcony: canister, gauges, and the service port it connects through. That port is opened at every refill, which is what makes its valve core a wearing part and an easy one to check past.

What else produces this

A leak that survives repeated inspection is a search-order problem, not a mystery. The refill interval sizes it: two to three months to drain usable pressure describes something slow and steady. Working the circuit in order, from the main pipe joints inward, leaves the small service-port fittings last. That is where a standard leak check tends to stop short.

Three refills in under a year, each holding two to three months, fits a slow steady loss rather than a sudden failure.
Main pipe joints, pipe fittings and indoor coil connections all clear, which is why earlier visits found nothing.
Bubble solution and an electronic sniffer both register at the service-port valve core on the outdoor unit.
A core worn and slightly deformed by age and by being opened at every past top-up explains a seal that leaks only slowly.

Why it happens

The valve core is a wearing part that gets used every time the system is charged. Connecting to the port presses the core open and releases it, and each cycle costs a little of the sealing surface. After years and several top-ups the seal closes almost, but not quite, and refrigerant slips past slowly enough to take months to matter. The leak is too small to find without testing at the port itself, which is why a wider circuit check clears the system and the cycle repeats.

What resolution involves

The core is a small part, and the scope is the reassuring half of the answer. It goes in, then pressure goes in and has to hold before any refrigerant follows. A steady reading with no drop is what confirms the circuit is sealed. Only then does the recharge happen. No indoor coil work and no compressor work follow from this diagnosis.

How to tell it worked

Watch the size of the fix against the size of the fear. A repeat-top-up symptom quoted as a coil or a compressor deserves one question first: where was the leak located, and what named it.

Before you approve a quote

The leak can hide at the fitting used to add the gas

A leak that survives several inspections is usually a search-order problem, not a rare fault.
Service-port hardware wears from being opened, so the connection used for every refill is a candidate in its own right.
Ask what named the leak. A sealed circuit is proved by pressure that holds before recharge, not by cooling on the day.

Questions this case answers

Why does my aircon lose gas again a few months after every top-up?

Because refrigerant is not consumed. If cooling fades on a repeating schedule, gas is escaping and the top-up only resets the clock. Three refills inside a year fits a slow, steady loss rather than a sudden failure. One common source is the valve core inside the outdoor service port, worn just enough to let gas slip past.

Where do small refrigerant leaks usually hide?

At connections rather than mid-pipe. Checks along the main joints, the pipe fittings and the indoor coil connections often find nothing. The service port needs focused testing before it gives itself up, first with bubble solution and then with an electronic sniffer. The core inside wears and deforms with age and repeated use.

Does replacing the valve core actually stop the leak?

When the leak is confirmed at that point, yes. A matched new core goes in, then a pressure hold test runs before any gas is added. Pressure holding steady with no drop is the proof that the circuit is sealed, and only then is the system recharged. No indoor coil or compressor work enters the picture.

What should I ask before paying for another gas top-up?

Ask what named the leak, and whether pressure held before any gas went in. Pressure that sits still overnight is the proof; pressure that falls is the fault still open. Without a located leak, the next refill buys the same short window as the last one.

Describe your situation

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

WhatsApp us