Why Does My Air Conditioner Stink?

When you first crank up your home air conditioner after a long drawn out winter and spring season, you might be hit with a thoroughly unpleasant, toe curling smell wafting up out of the vents. Don’t panic, it is normal for any electronic unit to have a few kinks after a long idle period. The smell could have a number of surprisingly innocuous causes – some that you would be advised to act on immediately if the offending smell doesn’t drift away soon.

Stagnant Water

When water mixes with dirt or dust and sits out for a long time it often starts to smell. Moisture that was trapped in the air conditioning unit could be the cause of an off-putting stink from the vents when you turn it on after a while. Also, standing water sometimes leads to the growth of mold, which also has a strange and unpleasant odor and can have a variety of adverse health implications if not dealt with swiftly and efficiently.

Rusted Parts

Sometimes the inner parts of the air conditioner, like the evaporator coils, become very rusty. Rust, which often forms due to water aging on the various metal parts, lets off an unpleasant musty or metallic odor after some time. In some cases the smell goes away after a few uses of your air conditioner, but in other examples it only deteriorates as time goes on.

Something’s Lurking In There

Another possible reason for the smell from an air conditioner is that something small, like an insect or small animal, crawled in long ago and the little chap perished inside of the vents. Even some dead bugs let off foul smelling odors. If an animal carcass or bugs are somehow wedged inside of the air conditioner it is a smell that could persist for a long time until you remove the problem.


Not suprisingly you will want to eradicate the smell and fix your air conditioner, however a word of caution. If you don’t know what you are doing please consult a HVAC professional or a qualified and licensed handyman or tradesperson with experience in air conditioning units first.

If you do have experience with window air conditioning units and feel you have the confidence to proceed, take the air conditioner out of the window when not in use, and shake it a bit to check for standing water before putting it away. Water often gets stuck in window units when it rains or snows. If the smell is really bad when you turn it on and persists, unplug the unit, unscrew the casing and inspect the inside more thoroughly.

Remove any bugs or other matter inside. Wipe off any moisture or dirt or use a towel to soak up standing water. If the parts are rusty, a foaming cleaner might work, but you might want to consider simply purchasing a new unit if the current one is very old.

Whatever your decision, act quickly as you don’t want to be wearing a clothespin on your nose all summer!

This article brought to you by Edinburgh Homeforce, a tradesperson agency based in Scotland.

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