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AC service · Odour

How to remove a bad smell from a split AC

A musty or sour smell from a split AC usually comes from dirt and microbial growth on the wet indoor coil, the drain tray and the blower wheel. Clean the filter, foam clean the coil with Aerosure AC Foam Cleaner, clear the drain tray and pipe so water does not stand, and run the fan to dry the unit.

By · Reviewed by the InnovaChem technical team · Updated

Source
Wet coil, tray, blower
Clean
Aerosure AC Foam Cleaner
Also
Clear the drain
Car AC
Aerosure Car AC Vent Foam

Where the smell comes from

  • Indoor coil: dust on a wet coil feeds microbial growth.
  • Drain tray: standing water turns sour when the drain is blocked.
  • Blower wheel: sticky dust on the blades spreads the smell into the room.

The fix

  1. Isolate power and wash the filter.
  2. Foam clean the coil with Aerosure AC Foam Cleaner, following the 4-step SOP.
  3. Clear the drain tray and pipe so water flows out.
  4. Clean the blower wheel if it is dirty.
  5. Run the fan to dry the unit before cooling.

For cars, Aerosure Car AC Vent Foam reaches into the duct behind the vent slats.

Products used

Quick answers

Why does my AC smell bad when switched on?

Usually because of dirt and microbial growth on the wet indoor coil, a blocked drain tray or a dirty blower. Cleaning the coil and clearing the drain normally fixes it.

Why does a split AC smell musty?

Dust and moisture on the wet indoor coil, drain tray and blower wheel feed microbial growth. The smell comes out with the first air after the AC starts.

How do I stop the smell coming back?

Clean the filter every 1 to 2 months in the cooling season, keep the drain line clear, and foam clean the coil when it is dirty. Running the fan for a few minutes after cooling helps the coil dry.

Sources

  1. US Department of Energy, Energy Saver: Air conditioner maintenance

Related on InnovaChem

AC service guidesHow to clean a split AC coil with foam: 4-step SOPWhy is my split AC not cooling? A technician’s checklistAC service checklist for technicians (printable)How to clean an AC condenser coil (outdoor unit)How to find an AC gas leak before rechargingHygiene glossary

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AC maintenance numbers to know

Published guidance for room ACs. Follow the AC maker’s manual and the product label.
WhatTypical range
Clean or replace filtersEvery 1 to 2 months in the cooling season, sooner in dust [source]
Energy saved by a clean filter5% to 15% less energy than with a clogged filter [source]
Check the indoor (evaporator) coilEvery 12 months; clean when dirty [source]
Drain lineClear it at each service so water cannot back up [source]
Star labelCompare models by BEE star rating and ISEER [source]

What are the signs an AC needs a service?

  • Weak or uneven airflow from the indoor unit.
  • A musty or sour smell when the AC starts.
  • Water dripping from the indoor unit or a full drain tray.
  • Ice on the indoor coil or the copper pipes.
  • The AC runs longer to reach the set temperature, or bills go up.
  • New rattles, hissing or buzzing from either unit.

What should be in your service kit?

  • Gloves and eye protection
  • Coil foam cleaner and a spray bottle of clean water for rinsing
  • Soft brush or vacuum for loose dust
  • Fin comb for bent fins
  • Drain bag or sheet to catch runoff
  • Wire or blower to clear the drain line
  • Torch, screwdriver set and a way to confirm the power is isolated

Carry the product SDS on your phone and follow the AC maker’s manual for the unit you are servicing.

Standards and references

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