What Is an Aircon Chemical Overhaul?
Does your aircon still smell sour, even straight after a service? That’s usually the moment an aircon chemical overhaul is worth a look.
Aircon Servicing Ang Mo Kio is the local service of Cool Earth Aircon, which Brian started in 2007 as a one-man workshop. Since then, one pattern has held true: the worst grime hides where a quick wipe can’t reach.
An aircon chemical overhaul is the deepest clean a unit can get. The technician takes the fan coil unit apart on site and works through it part by part. Each one is cleaned, checked for wear, put back together and tested.
- Fan motor: checked for grinding or wear
- Blower wheel: where mould cakes between the blades
- Evaporator coil: cleaned of the film that blocks cooling
- Drain pan: where sludge packs into the corners
- Housing: cleaned and refitted
It goes further than a chemical wash, where the unit stays on the wall. Once the parts are out, we can reach the sludge in the drain pan and the mould on the blower wheel. Parts that can be soaked go into a chemical immersion to loosen what brushing alone will not shift.
Two Singapore guides show how the jobs differ. Helpling puts a wash at 1 to 2 hours per unit, every 6 to 12 months, and an overhaul at 3 to 5 hours, every 3 to 5 years. Billy Aircon describes a wash as partial dismantling, with only the front panel off. Exact timings vary by company and unit, so ask us when you book.
| Chemical wash | Chemical overhaul | |
|---|---|---|
| How much comes apart | Front panel and easy-to-reach parts | Whole fan coil unit, every part cleaned |
| Typical time per unit | 1 to 2 hours | 3 to 5 hours |
| Suggested frequency | Every 6 to 12 months | Every 3 to 5 years |
When Is an Overhaul the Right Job?
An overhaul makes sense when normal servicing no longer brings the cooling back. Book one when:
- There is a strong sour smell every time the unit runs
- Black mould or dark flecks blow out of the vents
- Jelly sludge sits in the drain pan or keeps choking the drain
- The unit is older than 5 years and has never had a deep clean
- The unit has gone more than a year without any service
As a rule of thumb, both Helpling and Billy Aircon suggest an overhaul every 3 to 5 years, with a wash in between. Billy Aircon also points out that if a unit still smells or leaks after a wash, the problem is sitting deeper inside.
If the smell is mild and cooling is only a little weak, a chemical wash from S$80 per unit is usually enough. Not sure which one fits? WhatsApp a photo of the vents and we’ll tell you before you book.
Got 2 to 4 units at home? You don’t have to overhaul them all at once. Send a photo of each unit’s vents, and we’ll say which ones really need it.
Why Does Build-Up Get This Bad?
Aircon units in Singapore run almost every day, and the air they pull in is wet. The Meteorological Service Singapore puts mean annual relative humidity at around 82%. It sits above 90% just before sunrise and only drops to about 60% on dry afternoons.
Here’s what that does inside your unit:
- Moisture from the coil drips into the drain pan.
- Dust and mould spores settle in that wet tray.
- Over time, the mix turns into a thick, jelly-like sludge.
- The sludge slows drainage, feeds the mould on the blower wheel, and pushes a sour smell into the room.
iCare Aircon, a Singapore installer, describes this sludge as algae and bacteria mixing with household dust. Once it reaches that stage, washing from the outside only clears the surface.
Older HDB Blocks in Ang Mo Kio
Many HDB flat blocks in Teck Ghee, Cheng San, Chong Boon and Kebun Bahru were built in the late 1970s and 1980s. HDB’s Ang Mo Kio Town Design Guide, completed in 2024, dates the town’s first slab blocks to 1973. By the early 1980s, the town centre covered 29 hectares.
A lot of these homes still run older units, some of them non-inverter systems on R22 refrigerant, with old copper piping behind them. R22 is being phased out, and Coogle Aircon says supply is limited while costs keep rising. That makes a proper inspection worth doing before you spend more on an old unit.
Older blocks along Ang Mo Kio Avenue 3 and Avenue 10 often need an overhaul when routine servicing no longer restores the cooling. While the unit is open, we also check the pipe insulation and the drain connection, since worn insulation on old piping is a common source of drips.
Common Problems We Solve
Strong sour smell
A sour smell points to sludge and mould deep inside the unit, usually in the drain pan and on the blower wheel. Taking those parts out and cleaning them is what removes the source.
Black mould blowing out
When dark specks land on the bed or the wall below the unit, the blower wheel is shedding mould as it spins. Each blade needs a proper clean, which is only possible once the wheel is out.
Jelly sludge in the drain pan
Sludge blocks drainage and causes overflow onto walls and floors. The pan is removed, soaked and scrubbed so the water can drain freely again.
Installers such as iCare Aircon describe pulling large sludge clogs out of the standard 13mm or 16mm PVC drain pipes. For leaks with other causes, see water leak repair.
Severe loss of cooling
If a unit barely cools even after servicing, a heavily coated coil and a clogged blower wheel are common causes. When the overhaul does not bring the cooling back, the next step is to check refrigerant and parts through not cold repair.
Is a Worn Part Found Along the Way?
Because every part comes out, the overhaul is a good moment to spot wear. Here’s what we look out for:
- A fan motor that has started to grind
- A cracked drain pan
- Worn pipe insulation on older copper piping
Billy Aircon suggests getting a unit that makes loud mechanical noises inspected, as it may need an overhaul. Anything worn is shown to you and quoted before work. Nothing is replaced without your go-ahead.
A Mitsubishi Electric unit, a Daikin unit or an unbranded older unit all get the same check. For replacement units, enquiries go to Cool Earth Aircon at coolearth.com.sg.
After the Overhaul
An overhauled unit starts clean, but the same humid air keeps passing through it every day. To stop the sludge and mould from building up again, book general servicing every 3 to 4 months. Alvaircon calls this the general rule of thumb for Singapore homes.
Each visit covers three jobs:
- Cleans the filters
- Checks the coil
- Flushes the drain line, which is where the trouble starts
Manufacturer manuals often assume a 4 to 6 month gap, but aircons.sg says debris builds up 2 to 3 times faster in Singapore’s climate. That’s why shorter gaps pay off.
If remembering to book is the hard part, an annual maintenance contract schedules four visits a year with priority booking. Our guide on how often to service your aircon explains why that interval suits units in Singapore homes.
Ready to book an aircon chemical overhaul, or still comparing? See the full price list to compare the overhaul with other services, then WhatsApp us a photo of your vents to get started.
