Aircon Smells Bad? Here’s What It’s Telling You

If switching on your aircon releases a musty, sour, or chemical odor, it’s not something to mask with air fresheners. Smells are symptoms. Whether it’s mold, bacteria, stagnant water, or chemical discharge — the source needs to be located and fixed. Here’s how we diagnose it.

What’s Causing the Bad Smell from Your Aircon?

1. Mold or mildew inside the unit

Singapore’s humidity makes your fan coil the perfect breeding ground. Moisture + dust = biofilm. The smell: musty or wet-sock-like.

2. Blocked drainage line or stagnant water

If water isn’t draining properly, it pools in the tray. That buildup breeds bacteria. The smell: swampy, sour, or stale.

3. Dirty air filters

When filters are clogged, dust collects moisture and grows bacteria. That smell circulates through your entire space.

4. Microbial growth on evaporator coil

If the coil is never deep-cleaned, microbial buildup takes hold. The smell: damp, sometimes sharp or vinegary.

5. Refrigerant leak

Chemical smells (like nail polish remover or sweet-sour odor) can point to a gas leak — especially in inverter units.

6. Incorrect or incomplete cleaning

If coil wash is done without drying or proper drainage, leftover moisture worsens odor over time.

7. Poor ventilation

In rooms with weak airflow or blocked vents, stale air can trap and magnify odors coming from the unit.

What You Can Check First

• Smell starts only when the aircon turns on?

• Strongest near indoor unit or also near vents?

• Filters recently cleaned?

• Drain pipe dripping steadily?

Don’t spray perfume or air freshener — that only masks the issue, not fixes it.

Why It Matters

Odor signals bioactivity. Left untreated:

• Mold spores may circulate into the room

• Bacteria-laden condensate can overflow

• Gas leaks may go unnoticed

• Occupants may experience irritation or allergic response

Every smell has a source. It needs to be located and neutralized — not ignored.

When to Book a Diagnostic

✅ Smell starts only when aircon runs

✅ Filters already cleaned, but smell persists

✅ Drainage tray hasn’t been checked recently

✅ Chemical or sour odor near vents or unit

We’ll assess the drainage, coil condition, and gas circuit — and recommend the right treatment, not a guess.