Why is my aircon making noise?
Each aircon noise points to a different part. Rattling usually means something loose, buzzing an electrical part such as a capacitor, repeated clicking a relay or PCB, squealing a worn fan motor bearing, and gurgling a partly blocked drain. Grinding is often a rubbing blower fan: switch off and have it checked. A soft start-up click is normal.
Key takeaways
- Some sounds are normal: a soft click at start and stop, light creaking and a brief hiss as refrigerant settles.
- Grinding means stop: a blower fan rubbing the casing can crack or burn out the fan motor if left running.
- Outdoor buzzing with a still fan is electrical: it is often a capacitor or contactor, and repeated restarts strain the compressor.
- Dirt causes noise too: uneven dirt on the blower fan unbalances it, and servicing fixes that.
In the video above, Uncle Eric shows how a jammed blower fan is removed from an indoor unit, one of the noisier faults we see.
How do I work out what the noise is?
- Find the source. Stand near the indoor unit, then near a window facing the outdoor unit. Indoor noise is usually the blower fan, panels, louvres or drain. Outdoor noise is usually the fan, compressor, bracket or electrical parts.
- Note when it happens. If it is only a soft click or short hiss at start and stop, it is normal. If it is continuous or getting louder, go on.
- Indoor grinding, scraping or thumping: switch off now. The blower fan is likely rubbing, cracked or jammed. Grinding right now? Message Luna on WhatsApp.
- Indoor rattling: check the front panel is clipped shut, the filters are seated and nothing is touching the unit. If it continues, something inside is loose.
- Indoor gurgling: check the drain outlet and watch for drips. Gurgling often comes before a water leak.
- Outdoor buzzing with the fan not spinning: switch off. This often points to a capacitor, contactor or fan motor fault.
- Continuous hissing near the pipes, with weaker cooling: possible refrigerant leak. Low gas always means a leak somewhere: see signs of an aircon gas leak.
What does each aircon sound mean?
Sound | Indoor or outdoor | Usual causes | DIY or technician |
|---|---|---|---|
Rattling | Either | Loose panel or screws, debris in the fan, outdoor unit loose on its bracket, pipes touching the wall | Check panels; rest technician |
Buzzing or humming | Usually outdoor | Capacitor, contactor or motor fault; loose wiring | Technician |
Repeated clicking | Indoor | Relay or PCB fault, louvre motor gear slipping | Technician |
Squealing or screeching | Either | Dry or worn fan motor bearing | Technician |
Gurgling or bubbling | Indoor | Partly blocked drain with trapped air | Check outlet; technician to clear |
Continuous hissing | Either | Possible refrigerant leak at a flare joint or valve | Technician |
Grinding, scraping or thumping | Usually indoor | Blower fan rubbing, cracked or jammed; failing fan motor | Switch off, technician |
Which noises are normal?
A soft click when the aircon switches on or off comes from the relay and louvre motor. Light creaking is plastic expanding and contracting. A short hiss or gurgle when the compressor starts or stops is refrigerant settling. A steady whoosh of air, louder on high fan, is normal too.
Rattling
Rattles usually mean something loose. Indoors it is often the front panel, an unseated filter or a small object in the fan. Outdoors it is often the unit vibrating on a loose bracket, a panel screw that has backed out, or pipes knocking against the wall. Tightening and re-securing usually fixes it.
Buzzing or humming
A low hum while running is normal. A loud buzz, especially from the outdoor unit while its fan is still, often points to a capacitor or contactor, or a motor struggling to start. Do not keep restarting it, as that strains the motor and compressor.
Clicking that does not stop
One click at start-up is normal. Clicking that repeats while running usually comes from a relay switching on and off or a fault on the PCB, and sometimes from the louvre motor's gear slipping. This needs testing with a meter, not guesswork.
Squealing or screeching
High-pitched squeals usually come from a fan motor bearing that is drying out or worn. They get worse until the motor seizes, so replacing the motor early costs less than waiting for it to fail.
Gurgling or bubbling
Gurgling from the indoor unit is often water struggling through a partly blocked drain, with air bubbling back up. Clearing the drain early usually prevents a leak.
Why do blower fans jam, rub or wobble?
The blower fan is the long, barrel-shaped part in the indoor unit that pushes air into the room. Dust and slime collect unevenly on its blades, so it becomes unbalanced and starts to wobble, hum or knock. Over time it can shift on its shaft, rub the casing or crack. A jammed blower fan has to be removed from the unit to free it, clean it or replace it.
That is why we take the blower fan out and clean every blade with PowerJet during premium servicing. A chemical wash also takes the blower fan out and PowerJets every blade back to as-new. For an extremely soiled unit, a chemical overhaul dismantles and cleans every part, as a last resort. Watch: Mitsubishi Heavy Industries aircon not cooling, weird noise fixed.
Outdoor units have their own common faults, covered in our post on outdoor unit problems in Singapore homes. For how the indoor and outdoor parts work together, see how an aircon works and where it goes wrong.
Do not open the unit or climb onto the aircon ledge to look for a noise. Both are jobs for a trained technician.
What it costs
Job | Price | What drives it |
|---|---|---|
Diagnosis visit | S$150 per visit | Flat fee per visit; parts and repair extra |
Premium servicing with PowerJet (blower fan cleaned) | S$80 for one unit | Unit type |
Indoor fan motor replacement | Quoted after the S$150 diagnosis | Brand, model, part availability |
Outdoor fan motor or capacitor replacement | Quoted after the S$150 diagnosis | Brand, model, ledge access |
PCB replacement | Quoted after the S$150 diagnosis | Indoor or outdoor board, brand and model |
Re-securing the outdoor unit or bracket | Quoted after the S$150 diagnosis | Ledge access, bracket condition |
When to call a technician
Call us if you hear grinding, scraping, loud buzzing, continuous hissing or squealing, if the noise is getting worse, or if it comes with weak cooling, a burning smell or water. Our aircon repair team can find the source and fix it, with a repair warranty from 180 days (servicing carries 90 days).
You can book online in under a minute, or chat with Luna, our AI assistant, on WhatsApp any time.
Frequently asked questions
Is it safe to keep running a noisy aircon?
A soft click or brief hiss is fine. Grinding, loud buzzing, burning smells or a fan that sounds like it is hitting something are not, and running the unit can turn a small repair into a motor or compressor replacement. Switch it off and have it checked.
Why is my aircon louder at night?
Usually it is not louder, the room is just quieter. Night is also when many people run the aircon for long stretches, which makes small rattles and clicks easier to hear. If a sound is new, note when it happens and tell the technician.
Can servicing make my aircon quieter?
Often, yes. A dirty, unbalanced blower fan, clogged filters and loose panels are common causes of noise, and all are dealt with during a proper service. Worn bearings, failing motors or a noisy compressor need a repair instead.
Can I oil a squeaky aircon fan myself?
It is not recommended. Most indoor fan motors use sealed bearings, so the unit has to be dismantled to reach them, and spraying lubricant inside can attract dust or reach electrical parts. A squeal from a worn bearing usually means the motor needs replacing.
How long does a noise repair take?
Tightening loose parts or cleaning an unbalanced blower fan is usually done in one visit. Replacing a fan motor, capacitor or PCB depends on the brand, model and whether the part is in stock, and the technician will tell you before starting.
Eric Lim, aka Uncle EricFounder of iAircon.Repair, now in its 10th year servicing aircons in Singapore. Every job is filmed, so you can watch the work on YouTube.
