My air conditioner smells bad

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My air conditioner smells bad. Why?

How can the air conditioner smell so bad? If you’ve asked yourself this question before or are asking it now, it’s because you’ve had the unpleasant problem of your air conditioning smelling bad and ‘stinking’ as soon as you turn it on.

But what produces this smell?

The first thing that we must take into account is that common air conditioning machines suck or absorb the air from the room itself that they are going to air-condition, so if in this room odors are produced or reside, the air conditioning unit is going to move it through all the places where it will drive air.

“My air conditioner smells bad, when I turn on the air conditioner the whole house smells like a drain.“

This phrase, as a technician, has been said to me many times and the answer is always the same: the air-conditioning machine, by itself, does not produce odours. What happens is that the machine, if it is a duct unit, generally sucks the air from the top of the false ceiling, so if some kind of smell accumulates there, when the unit is turned on, it will move it and distribute it all over the house, giving the feeling that it is our air conditioning machine that smells.

So, the air-conditioning machine never smells?

No, our air conditioning machine can smell bad, but this smell, except in very specific and rare cases, is never produced by the machine, it is produced by other factors and ends up affecting the machine. Let’s see what factors can affect and produce that bad smell in our air conditioning unit.

Dirty filters

As we saw earlier, air conditioning filters are one of the few, if not the only, things we need to service regularly. This maintenance, apart from being very simple as we explained before, is not done for nothing, this maintenance and cleaning of filters will help us as we have already seen to keep our air conditioner in the best possible conditions, avoiding possible breakdowns, reducing consumption and also avoiding and mitigating those unpleasant smells.

And why do the filters smell?

Actually the filters do not usually smell, the filters perform their function of air filtering and trap in the mesh from which they are made, a multitude of particles that exist in suspension, preventing these particles from reaching the interior of the unit and therefore, preventing it from getting dirty inside.

But what happens when the filters are not cleaned properly?

What happens is that the filters become clogged and saturated, preventing them from performing their function properly and causing that dirt to pass little by little into the interior unit and therefore filling it with dirt. This dirt in combination with the humidity produced in the exchanger and the interior fan when operating in cold mode, will cause a multitude of bacteria and fungi to proliferate in these places which will give rise to the typical smell of ‘humidity’ with touches of ‘vinegar’ so characteristic of air conditioning units that have poor maintenance.

How can I avoid this smell?

First and foremost, by cleaning the filters periodically. But how often? This question and its answer are very relative, it will depend above all on the amount of use we give to our air conditioning. There are air conditioning units that work very little time and others that never stop, therefore, it will depend on the amount of use we give it, but at least we will need a visual revision at least every 6 months or 1 year and depending on the result of this revision, we will proceed to clean or not the filter.

Once our air conditioning smells bad, the solution is to do a deep cleaning. Both to the filters, fan, exchanger and in general to the whole interior unit, letting it dry and spraying, if considered necessary, some product that eliminates bacteria and fungi. For example, the Tidas system of Caramba or if you are looking for something more economical the Faren F20 that for about 15€ can solve this problem, you can purchase this disinfectant here.

Dirty fan and cold exchanger

As we have mentioned, when an air conditioning unit is not properly maintained, no matter how small, this has consequences in the long run, among them, not cleaning the filter of our air conditioner will cause accumulated dirt to pass through the filter and accumulate in the rest of the indoor unit, places that are much more complicated, expensive and difficult to clean.

Two of the places or ‘pieces’ that get very dirty when this happens are the cold exchanger and the interior fan and this, together with the humidity produced by the unit in cold mode, makes it become like a ‘wet paste’ where bacteria and fungi proliferate, producing such an unpleasant smell that it smells as soon as the unit is turned on but after a while, when it gets cold, it disappears. This smell is not that it disappears, goes away or is eliminated, this happens because when it cools down and produces water droplets – condensing humidity – this humidity creates like a protective barrier that prevents us from smelling it but once it stops throwing cold and therefore condensing humidity, it will return with more and more intensity.

Indoor unit drainage

The drainage of the indoor unit can also ‘produce’ odours. Let’s see why.

All air conditioning units have a drainage system because they all condense moisture when they ‘cold’. They condense humidity and this generates water, this water has to be expelled somewhere and the drainage of the interior unit takes care of this, of leading this water somewhere.

Vacuum the smell from another drain

If the option we chose was to drain this water into a carafe with a pipe, we are not going to have problems with odors from aspiration. But if we have connected this drain to a drain in the house then we may have an odour problem, as odours from the general drain can travel up to our air conditioning unit.

To avoid this problem, simply place a siphon in this pipe before it is connected to the house’s main drainage system. This will prevent the smell from ‘traveling’ from the main drainage system to the indoor unit and distributing the smell throughout the house. As if this were not enough, we will also be protecting our machine from future gas leaks produced by these gases and vapours, as this is one of the most common and least known causes of gas leaks in our air conditioning equipment.

If you want to see the most common causes that can produce gas leaks in our air conditioner, you will surely be interested in this other article.

Most common gas leaks in our air conditioning

Not enough slope in the drain

Another flaw in the design of the indoor unit drainage is that it does not have enough slope to drain properly. If this happens, water will accumulate in the tray of our indoor unit and this can degrade and generate bad odor.

Other possible causes of my air conditioner smelling bad

The above points are largely responsible for the overall bad smell of an air conditioning unit, but there are other factors that although less common and sometimes very rare, can also produce bad smells. We will briefly mention some of them:

• Plastic or rubber from the indoor unit itself that comes with odors from the factory.
• Odours that are transmitted from the wall chamber of the dwelling to the interior of the dwelling – bad sealing of the hole and odour-absorbing insulation of the chamber-.
• Air fresheners inside the air conditioning.
• Our indoor unit -ducts- sucks air from the false ceiling and there is some kind of leak in the house’s drain.
• Our air conditioning unit draws air from a neighbor’s false ceiling.