On those hot days, one of our best friends becomes the air conditioner. Without complaint, it fires up and cools us down, allowing us to recharge our sun-soaked bodies and bring our body temperatures down enough to get a sound night's sleep. There are times, of course, when the HVAC system starts to fail, namely when the air that's pumped out is warm instead of the bitter cool that we've grown accustomed to. There are a number of issues that could cause an A/C to blow out warm air such as a bad compressor or lack of refrigerant. Unfortunately, warm air isn't the only pitfall that can befall an air conditioner, and others can be somewhat worse – an A/C that spits out a breeze that stinks.
A foul-smelling odour coming from the A/C can become almost unbearable even if the air is still cooled. Plus a stench from the unit is not normal and is a sign of something not up to par within the system. There are a number of issues that could be causing the stench and will possibly require air conditioning repair service including:
Your Air Conditioner Isn't the Correct Size
Most homeowners are aware that the air conditioner cools the house obviously, but it also performs a very quintessential second function of dehumidifying. At the same time the a/c removes heat from the air, the a/c also removes moisture. Some people assume that bigger air conditioners are better at cooling rooms. While that's partially true, having an air conditioner that is too big for the room doesn't allow it to do a full cycle, and thus not remove enough humidity from the air.
A cold room could be a front for an unhealthy room when the A/C is too large for the area it's cooling. On hot days when humidity builds up in the room, mold and mildew will cling to the moisture of the air conditioner and start to grow on its components. As the air passes through these moldy components to get delivered to the room it spreads mildew spores and carries a dirty sock smell with it. In these instances, either run the dehumidifier longer or level down to an A/C that is more suited for a room of that specific size.
You Have a Clogged Condensation Drain
While the dehumidifying aspects of an air conditioner are nice, they do attribute to many of the smells associated with a cooling unit. Another instance where this happens is when the condensation drain backs up. When the air conditioner is running the evaporator coil gets very cold, almost forming a frost layer. As warm air from the house passes over this coil, the frost starts to condensate and drain into a pan outside the house. When sediment builds up in this pan, it gets clogged and therefore the liquid condensation has nowhere to go, become a cesspool for mold and mildew to grow. Once again this mold gets passed through the room in the stench of a dirty sock.
While it's pretty easy to clear out the drain with a sharp thin object, if that doesn't solve the problem of leaking water you may need to bring in an air conditioning repair service. What might have happened is the pan gets cracked and needs replacing, but a professional will give a definitive diagnosis.
Internal Coils Are Dirty
An air conditioner works by passing warm air over cooling coils that chill it before sending it into the room. One reason that a smell occurs is when these internal coils have become embedded with dirt or bacteria. The air crosses over these coils directly before being distributed to your room so the breeze will pick up the smell from this debris, and it is noticeable. The easy fix is to unplug your a/c and spray down the inner components with compressed air. It's also wise to spray down the unit before installing it for the summer to help remove some of the dust that has built up over storage.
Clogged Filters
When air cycles through the air conditioner, it first passes through a filter to make sure it's somewhat cleaner for human consumption. Obviously if this filter is clogged or embedded with gunk there will either be less air that passes through or it will pick up the smell and stench of the grime it just passed through. These filters should be changed out at least once a month while the air conditioner is constantly running or cleaned if they are the spray-off type. The dirty filters not only produce a stench in the house, they also make the a/c work harder and thus drive up utility bills.
Dead Animal in the Unit
Mold isn't a bad scenario to deal with, compared to a dead animal at least. It's a rare occurrence, but animals have been known to die either in the outside air conditioning unit or the vents inside. Rats, possums, or birds in the ventilation system are a nuisance, a very smelly one. You'll want to get rid of these expired critters as soon as possible not only because they are annoying but because they may carry adverse health risks with them. If you find a dead animal in the vents, it may be best to call for an air conditioning repair service. Not only so you won't have to touch the varmints, but because removing sections of ductwork is required to find the animal. It may cost you hazard pay but will be worth having comfortable temperatures in the home without old rat smell.
One final thing to remember is that most air conditioners don't smell, and the sign of an odor means something is amiss.