homeowner plugging nose due to air conditioner smell

When an air conditioning system is running well, the air blowing through the vents should smell normal. It should not have an unusual or foul smell. If you smell an unpleasant, offensive, or strange odor, it is a sign that something is wrong with your HVAC system. If this is the case, you should contact an HVAC technician to inspect your unit right away. An air conditioning technician who specializes in maintenance and repairs can help detect the cause of the unpleasant smell. Likewise, they will let you know what can be done to remedy the air conditioner smells.

Determining The Cause Of Unpleasant Air Conditioning Smells

This article includes information regarding the cause of a variety of foul odors caused by air conditioning units.

Air Conditioner Mold Odor

image of mold that was on air conditioner

A common problem reported by homeowners is experiencing a stale or moldy smell when turning on their air conditioning unit. This unpleasant musty smell is usually caused by water that has accumulated in the drain pan, drip lines, or ducts. The buildup of moisture along with undesirable temperatures creates the perfect environment for fungus, mildew, or mold growth. The thriving microorganisms are responsible for the unpleasant odor.

Clogged or dirty air filters are another common cause of unpleasant HVAC system-related odors. This is true, especially for homes located in a hot and humid climate. When moisture develops in the air filter, it leads to the unpleasant smell of stale air. This is true, especially if the air conditioning system has not been in use for a while. However, if the air filter is the problem, you will notice the unsavory smell filling your home after you turn on the air conditioner.

Solution: Empty the air conditioner drain pan on a regular basis. If emptying the drain pan does not get rid of the smell, contact an HVAC technician. Ask them to come and inspect your air conditioning unit. A professional can inspect your central air conditioner unit, lines, and ducts to determine what is causing the problem. If water has accumulated, your unit might be leaking. This is why it is important to have regular AC tune-ups. If the water is not draining properly, a technician will be able to repair the air conditioning problem. If you have your AC unit inspected each year, the annual air conditioner tune-up will prevent these types of problems from occurring.

Smelling Cigarette Smoke After Turning On Your Air Conditioner

If anyone in the home smokes cigarettes indoors, the smoke particles accumulate after being trapped in the air filter. Every time someone is smoking in the house, the filter will trap a greater number of smoke particles. When the air conditioner is running, it will force the air through the filter. This will loosen the particles and pushing out the cigarette smoke smell through the air vents. You may begin to smell cigarette smoke throughout the house even when nobody is currently smoking indoors.

Solution: Do not smoke inside of your home or only smoke next to an open window to reduce the cigarette smell. Use a high-quality air filter and change it each month. If you have a reusable air filter then you should clean it thoroughly every month to get rid of the smoke particles. Dusting the air conditioning unit each week can also help to remove dust and smoke particles so they do not become trapped in the filter. Scheduling air conditioner maintenance each spring is a great way to ensure that your unit stays in good condition and a professional can recommend the best filter for your home.

Your Air Conditioner Unit Emits An Unpleasant Burning Smell

image of electrical wires in an air conditioning system

If you smell a burning smell after turning on your air conditioning unit, it could mean that some part of your air conditioning unit is damaged. It could be a burning wire or cable or the actual motor of the unit that is the problem. If you have not turned your air conditioner on for a lengthy period of time the smell could simply be due to an accumulation of dust being exposed to high heat. If this is the case, the burning spell will be temporary. However, if the smell continues then you should turn off the AC unit and call an experienced HVAC tech to come and look at your unit to find out what is causing the odor.

Solution: Do not try to repair your air conditioning unit if it is producing a burning odor. It is important to contact an HVAC technician who can safely make the necessary repairs.

Air Conditioner Emits A Rancid Odor

If you detect a disgusting, rancid smell after turning on your AC unit, you might be dealing with a decomposing animal that has found its way into the A/C system and died. Decomposing animals produce gases such as methane and sulfur dioxide that produce very strong odors, which are easily detectable. The odor is so pungent that it can cause gagging or vomiting.

Solution: Locate the dead animal that is inside of your air conditioner or air ducts so that you can remove it. Clean and sanitize the area well making sure to remove all of the organic matter. If you do not want to deal with such an awful task, you can contact an HVAC professional who can help you. If you have your AC unit checked by a professional technician annually, you can have your system cleaned and inspected as well as receive advice on how to protect your unit from pests.

Detecting The Odor Of Gas

Methyl mercaptan depicting natural gas leakIf you detect the odor of rotten eggs or cabbage or hydrogen sulfide you may have a potentially hazardous gas leak. Although natural gas is odorless, manufacturers have added a chemical called mercaptan to natural gas that gives off a distinctive strong smell so people can recognize a gas leak quickly and take immediate precautions. Gas poisoning due to a leak can cause headaches, nausea, weakness, suffocation, coma, and death.

Solution: If you detect the odor caused by a natural gas leak, leave your house immediately. Make sure all members of your household go outside into the fresh air right away. Call the fire department for advice. They will let you know what to do. Likewise, they can come to your house to check the gas levels and turn off the gas supply. If you are experiencing any feelings of sickness, call your local emergency services. Ask them for advice or an ambulance if emergency care is needed. Make sure you wait outside of your house for help to come. A natural gas leak can cause an explosion when exposed to sparks or fire so do not light anything up before leaving your home.


Although your air conditioning unit can produce different smells for a variety of reasons, in many cases, the odors are harmless. However, unpleasant odors should never be ignored. They are a sign that there is a problem with your A/C unit. Although some odors are easily eliminated with a filter replacement or quick cleaning, others may not be so easy to fix. An HVAC professional can help to prevent problems that lead to unpleasant odors and even potential health problems. Regular air conditioner maintenance can also prevent deterioration of your system. This way, you can avoid having to make expensive repairs.

Contact Tower Energy for Your HVAC Needs

Tower Energy LogoTower Energy offers reliable service to those in Hartford County, Connecticut. We employ highly qualified technicians who offer HVAC system installations, repairs, tune-ups, and replacements. All of our technicians are certified, knowledgeable, and capable of providing superior HVAC system services.

Tower Energy offers the best heating and cooling servicing prices available in the area. Our trustworthy services will not only improve the comfort you experience in your home but also improve energy efficiency. This helps to protect the environment and reduces your energy bills. If you need an HVAC technician to repair or replace your system, our experts can recommend the best unit for your home within your budget. We guarantee our work to make sure you are completely satisfied with our service. You can make an appointment by calling Tower Energy today and you will receive a free in-home estimate.

Contact us now or call us at (860) 677-7347 to find out more.