Why does your a/c unit smell?

K EDWARDS • October 9, 2023

At Bedfordshire Air Conditioning we are often asked about smells from Air Conditioning systems. It’s not a pleasant subject and it’s quite subjective too as, what one person finds unpleasant another person may not, and what someone can smell quite strongly, someone else might not be able to smell at all.


However, usually a smelly air conditioning unit can be attributed to several factors:


  1.  Mould or Mildew: the evaporator coils and other parts of the indoor unit can accumulate moisture or condensate over time, creating a damp environment that’s conducive to the growth of bacteria, mould and mildew. These micro-organisms can produce unpleasant odours.

  2.  Clogged Drain Pipe, or pump: a clogged drain line lead to water build-up in the unit, creating a breeding ground for bacteria, mould and mildew. The stagnant water can emit musty smells.

  3. Dusty Filters: if the air filters are dirty, they can become a source of odours as dust, dirt and debris accumulate on them.

  4. Stagnant Water: water that doesn’t properly drain or evaporate can become stagnant and emit bad smells.

  5.  Chemical Odours; sometimes, a chemical or burning smell can indicate a problem with the units electrical components, or wiring. Be aware of this one and call us out straight away if you experience this!

  6. Outside contaminants: if outdoor air pollutants enter the unit, they can contribute to bad smells circulating through the system.

  7.  Inside contaminants: remember your air conditioning unit will, in the main, only recirculate air already in your room. If you have food which has gone off in the office somewhere, or a water-logged pot plant where the soil has become stagnant/sour or perhaps if your return air grille is positioned too close to a kitchen or the toilets (yes; we have had all of these situations in the past!) then your a/c unit may simply be circulating odours which already exist within the room.


To address these issues, consider the following steps:


  * Regularly clean or replace air filters

  *   Keep the unit maintained and clean, including the evaporator coils and drainage system. Your unit may need a biocide application - ask us what this means!

  *   Use a professional HVAC company – like Bedfordshire Air Conditioning – for regular maintenance and inspections.

  *   Run the fan on the unit for a while after turning off the cooling, to help dry out any excess moisture - this is easy and can be done by anyone. In fact, a lot of modern a/c units have this function automatically.


If the sell persists or seems unusual, it’s a good idea to consult with us to diagnose and address the specific cause of the odour. Why put up with a smelly a/c unit?







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