Why Is Your Aircon Making a Hissing Noise?

A hiss from a running aircon is one of the few noises that is almost always meaningful. In most cases it is refrigerant escaping through a small breach.

Where leaks usually start

Flare connections at the fan coil, corrosion pinholes in the evaporator, and vibration wear where piping passes through a wall are the three common origins in Singapore installations.

Why a top-up alone is not a repair

A sealed system does not consume refrigerant. If pressure has dropped, gas has gone somewhere. Adding more without locating and sealing the breach means paying for the same gas twice — and running the compressor under-charged in the meantime, which is what actually kills it.

What a proper diagnosis looks like

• Pressure readings taken at the service port
• Nitrogen or electronic leak detection to locate the breach
• Repair or component replacement
• Vacuum and recharge to the manufacturer's stated weight
• A verification run with temperature differential measured

Other causes of hissing

A partially closed service valve or an expansion valve working hard can also hiss. That is why the diagnosis matters more than the symptom.