What to Do About Bad Air Conditioner Smell

It happens every Spring as soon as the weather is warm enough. 

Homeowners turn on their central air system and there’s a smell. Whether it’s a chemical smell, a burning smell, or even a rotten smell, it’s canceling out the comfort of your system and it could be a sign of a minor nuisance or a major problem.

With over thirty years of experience in Lancaster County HVAC, we’ve seen every type of air conditioner problem, and we have experience identifying problems within any type of home air conditioning system. Below we outline what to expect based on the air conditioner smell you’re experiencing.

Why Does My AC Smell?

Not all smells are equally urgent when it comes to turning on your air conditioner. If you notice any chemical or burning smells, these are serious signs that your air conditioner may need to be evaluated by a professional. 

Other smells like musty, or even rotten smells sometimes represent minor issues that you may be able to handle yourself, and other times may still need professional help. Either way, the first thing you should do is try to identify the type of smell because it will help determine your or your HVAC contractor’s next best course of action.

What to Do About Air Conditioner Smell

What you’ll have to do, or whether you should contact an HVAC contractor will depend on the type of smell that you’re sensing. The smell from your air conditioner will help to inform you of both the problem and in some cases the potential solution as well. 

Below we’ll review the most common air conditioner smells, their sources, and solutions in order from “do it yourself” to “call a professional”.

Musty Air Conditioner Smell

One of the most common air conditioner smell complaints is mustiness. The good news is that musty AC smell can be an easy fix, but there are some red flags to look out for though.

If you have your AC unit in your attic a musty smell could indicate mold in your ducts. This can drastically lower the air quality in your house and even make you sick. If you have a musty, moldy, or mildewy smell and your AC Unit is in your attic you should have your system professionally evaluated for mold in the ductwork. Attic ductwork is particularly prone to mold if the attic is properly temperature controlled with insulation.

Moldy Air Conditioner Coils

If the problem isn’t in your ducts it could be on your air conditioning coils themselves. This is commonly referred to as “dirty sock syndrome” because that’s how the smell of the air is best described. It’s best to have your air conditioner coils professionally evaluated and either cleaned or replaced.

If after having your ducts and coils checked you notice the smell persists, you should check your air conditioner filter. Much like the filter on your car, or even a lawn mower, your air conditioner filter gets dirty over time from catching air particulates and contaminants. It’s best to change home air conditioner air filters seasonally (every three months) and this is an easy task that takes less than 10 minutes to do. 

If you’re not sure what size air filter you need, your current air filter likely has that information printed on its frame. And if you’re behind on air filter changes, don’t worry too much it just means the best time to do it is as soon as you can. 

Your local hardware store is likely to have the replacement air filter you need, and the whole process is sliding out the old air filter, sliding in the new one, and throwing the old one away. If you’re in the market for a new system, new advancements in whole-home air purifier technology have made clean indoor air an easy low-maintenance reality for thousands of homeowners.

Rotting Air Conditioner Smell

We’ll be honest of all the smells and fixes on this list rotting air conditioner smell is the least fun to deal with. The good news is that it’s likely not serious mechanical or electrical damage that is affecting your unit. 

The bad news is that the smell is probably caused by a dead rodent, bird, lizard, or other wildlife that made a nest within the unit itself over the winter or even within an air duct. You don’t need to be a professional to take care of the rotting air smell, but you will want some PPE in the form of gloves and a mask. 

You need to locate the source of the smell by finding out where its strongest. If the smell leads you to your unit outside, you’ll need tools to remove the cover and try to locate the dead animal or nest. If it leads you toward an air vent, will have to remove the vent cover to further investigate. We recommend having a flashlight handy. 

If you locate the source of the smell in the air vent you will want to remove it and dispose of it into a sealed garbage bag and take it outside. It would also be wise to wipe down the interior of the vent with disinfectant.

While this fix is more involved, and you could call an HVAC contractor to solve this problem if you’d rather not have to handle a decayed animal, there’s no professional or technical expertise needed for this fix. If the source of the smell is found in your air ducts, you may want to further investigate any potential holes and ensure that the ductwork is still sealed to help prevent repeat incidents.

Chemical Air Conditioner Smell

If running your AC is leading to a chemical smell there is a strong chance that your unit is experiencing a refrigerant leak. Refrigerant chemicals can be toxic to humans and the environment if overexposure occurs. If you’re noticing a chemical smell while running your air conditioning the first thing you should do is turn off your system. You do not want your system running because it may further exacerbate the chemical leak. 

After turning off the system, make sure to open any windows to ventilate the area you were smelling the leak. Finally, call an HVAC contractor to have your system evaluated as quickly as possible. 

Refrigerant leaks and line replacements are regular everyday work for certified technicians, but much riskier for homeowners to try and repair themselves.

Burning Air Conditioner

A burning smell is an immediate red flag that something is wrong with your AC unit. AC units are not powered by combustion engines so when functioning properly they should not give off any burning smell. If turning your AC unit on results in a burning smell, make sure to turn it off, and call for AC service immediately.

What’s likely is that your unit is experiencing an electronic failure within its circuit boards, compressors, or even power wires. This is not an easy fix and will require specific tools, knowledge, and replacement parts that are not readily available. 

For your and your loved ones’ safety, as well as the safety of your home, make sure to have a certified HVAC technician evaluate and repair your system before any further use.

Follow Your Nose

If you’re turning on your AC and noticing a smell, don’t try to ignore it and hope it will go away. Trust your senses, and investigate the source of the smell. Your ability to provide them with information from your own investigation will help them quickly identify and rectify the situation. 

At RSC Heating & Air Conditioning we have over thirty years of experience helping homeowners in Lancaster and the Greater Susquehanna Valley restore their central air systems to optimal working condition. 

Give us a call or request service today and our HVAC technicians will be happy to have your system smell-free in no time!

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