After a new aircon install: which noises are normal and which are not

A newly installed aircon sits in different conditions than the old one — new pipe runs, new bracket positions, new refrigerant charge in the lines. All of these can produce sounds that the previous unit did not make. That does not mean something is wrong. It means the system is running in a new physical context and some settling sounds are part of that.

Refrigerant flowing through new copper pipes makes a soft bubbling or hissing sound, especially in the first few days of use. This is the gas moving through the system under pressure. In most cases it quiets down once the system has run through a few full cycles. The same applies to light clicking sounds from the indoor head — these are often the PCB relay switching the unit between modes or fan speeds.

What homeowners are listening for in the first week is not silence — it is pattern. A sound that appears once, stays mild, and does not get worse is worth monitoring. A sound that grows louder over days, or that appears alongside weak cooling or a water drip, is worth reporting before the install context fades.

Soft clicks when the unit starts or stops are normal. The indoor head expands slightly under heat and contracts when it cools — the casing makes small cracking or clicking sounds as a result. This is more common in the first few weeks of use and typically settles down without any action needed.

A low hiss or gurgle from the indoor unit, especially right after the compressor starts, is the refrigerant moving into the evaporator coil. Some units — particularly Daikin and Mitsubishi models — produce a more audible flow sound than others depending on how the piping was routed. If the sound is quiet and steady, it is not a concern.

Dripping sounds from the outdoor drain area are expected in humid Singapore conditions. The outdoor unit produces condensation on the condenser coil during operation and that water drains to the ledge or tray below. This is not a fault — it is normal heat rejection in a humid climate.

Rattling from the indoor head — especially rattling that appears during operation and stops when the unit is off — usually points to a loose panel or a screw that was not fully tightened during install. This is a straightforward fix if caught early. Left alone, the vibration can cause the panel to crack or the screw housing to strip.

Vibration from the outdoor unit that transmits into the wall or floor is a mounting problem. The outdoor unit should be isolated from the wall bracket with rubber mounts. If vibration is felt through the wall in the room below, the mounts were either not fitted, fitted wrong, or not suited to the unit's weight. This needs to be reviewed while the install is still fresh.

A loud continuous hiss or a smell near the indoor unit is the one pattern to escalate immediately. Loud hissing combined with weak cooling can indicate a gas leak at a joint in the copper piping — usually at the flare connection where the contractor made the join. This is a workmanship issue and falls under the install warranty. Report it quickly.

When you report a noise, the most useful information is when it happens, not just what it sounds like. A rattle that only appears in fan-only mode points to a different cause than one that appears only when the compressor is running. A hiss that appears right after startup and fades points somewhere different from one that runs the whole time the unit is on.

Note whether the sound comes from the indoor head, the outdoor unit, or the pipe run in the wall between them. Indoor rattles are almost always a casing or mounting issue. Outdoor sounds are usually fan or compressor related. Pipe sounds tend to be flow-related and are more likely to be normal.

If you can, record a short voice note or video with the sound while it is happening. Installers diagnose noise from description more often than from inspection, and a recording removes the gap between what you remember and what you say.

Most install warranties in Singapore cover workmanship faults for a defined period after the job is done. Noise complaints that turn out to be installation faults — loose mounts, bad pipe joins, unsecured panels — fall under this cover. Raising them early keeps the conversation clear: the noise started after install, the install team can fix it.

Wait too long and the picture becomes harder to read. A loose panel that rattled from day one becomes ambiguous if it is raised after months of use. The installer has less reason to treat it as their scope. The first month is the window where noise patterns are clearly tied to the install context — use it.