AC Smells Musty

Gross smells in your house are never a fun thing, especially when they’re coming from your air vents and being circulated throughout the whole house. It isn’t uncommon for your air conditioning to produce an uncomfortable odor after months of disuse which is one reason why you should always blow out your AC unit at the start of the season and spend a few hours out of the house.

However, if it’s a consistent problem then something has to be done to fix it. Most musty smells are the result of mold or mildew which not only produce a bad smell but can potentially be hazardous to your health if you inhale and can exacerbate allergy and asthma issues. Before you call a professional to come fix it there are a few steps you can take to try and rectify the problem yourself that are quicker and cheaper.

Dirty Sock Syndrome

Before we talk about direct causes let’s talk about what has been dubbed as “dirty sock syndrome” which is what some people use to refer to the smell coming from the air conditioner. The biggest question most people have is “is the bad smell dangerous?” And the most likely answer to that is no, not usually.

Important: As a homeowner, realizing that you need to waste another Saturday waiting for the landlord or handyman to come over to fix another damaged appliance is frustrating. It shouldn't feel like the norm to constantly have damaged appliances and systems in your home since it can come to a huge cost at the end of each year.

The Home Improvement Solutions eBook covers everything you need to do in your home when it comes to maintenance and improvement so you can avoid wasting another weekend waiting for someone to come to your rescue.  

As stated before people who have asthma or allergies (or other issues along those lines i.e. poor immune system) are more susceptible to getting sick from mold or mildew. However, if the bacteria is growing specifically in your HVAC system, that’s when you will get into dangerous territory.

Before you get too worried, just know that the CDC states that mold is “mildly toxic” to the human body and the most extreme symptoms most people get are coughing and wheezing. Obviously, that isn’t great but it isn’t the worst case scenario. You’re going to want to get this situation handled as quickly as possible so read on to learn about ways to fix your potential “dirty sock syndrome”.

Important: As a homeowner, realizing that you need to waste another Saturday waiting for the landlord or handyman to come over to fix another damaged appliance is frustrating. It shouldn't feel like the norm to constantly have damaged appliances and systems in your home since it can come to a huge cost at the end of each year.

The Home Improvement Solutions eBook covers everything you need to do in your home when it comes to maintenance and improvement so you can avoid wasting another weekend waiting for someone to come to your rescue.  

Drain Line

One reason why your air conditioner may be producing a musty smell is that you may have a clogged drain line. You may notice your air conditioner shuts off or water is being built up inside the unit. If the drain pan accumulates stagnant water then it’s likely for mold of mildew to grow in the wet environment.

Thankfully, it isn’t too difficult to clean out the drain line yourself with common household tools. First, you have to turn off the circuit breaker to the unit for safety reasons. Then you want to identify the drain line which is outside by the AC unit. Find the opening to the unit (usually secured with a cap) and shine a flashlight inside to see if you can see any clogs in the line. If the clog is close to the opening you may be able to pull it out (wearing gloves or with needle-nose pliers).

Most other the blockages are further down the line and won’t be reachable, in this case if you have a wet vacuum you should be able to attach it to the line and suck the clog out. If you don’t have a wet vacuum you can always create a mixture of distilled vinegar, dishwasher soap, and warm (not hot) water and pour it into the line to try to eat away at the clog. This solution is also a handy thing to use to clean your drain line about once a month to prevent more blockages from forming.

Air Ducts

Another reason why your AC might be creating a musty smell is because your air ducts are leaking. You can usually tell this if you run your air conditioner for a long time but your home doesn’t cool down or your house is very humid. Also, if dust seems to accumulate more than usual this can be a sign because it isn’t being filtered out.

You can fix leaks in your air ducts pretty easily, the first thing you want to do is turn your AC on full blast (you may want to wear a mask that will protect you from mold and mildew spores). While your air conditioner is running you can check for leaks that are not obvious tears if you feel the air coming out. Pay specific attention to where two ducts are connected as these are common places for the duct to tear. Another thing to look for is duct tape as someone may have previously tried to repair the duct and the tape could have torn or come loose.

Once you’ve identified all the leaks you can use duct tape to seal up the holes but this is usually a temporary fix as it can wear out over time. A more efficient way to seal up the tears is to use mastic or duct putty (view on Amazon) which is a more permanent fix and thankfully pretty cheap.

Evaporator Coils

The last main reason why your AC may be producing a musty smell is because the unit has a dirty evaporator coil. If your airflow into the house is weak then it’s likely because there is something wrong with an evaporator coil. This can happen from residue build up or if the coil becomes iced over which you may be able to see when you look into your unit.

This is a very common problem because an evaporator coil produces 3 of the 4 things needed to grow mold; a dark housing, warm air, and moisture. When those things are combined with the fourth needed item, food for the mold (which can be found in dirt and dust) then your evaporator coils will grow mold.

You should absolutely leave the cleaning of evaporator coils to a licensed technician unless you have no other choice. You need confidence in your electrical skills in order to properly clean the coils without damaging your unit, but if you want to do it yourself here’s how. The first thing you need to do is shut off all power to the unit and the thermostat, turn off the necessary circuit breakers.

To get access to the evaporator coils you’re going to need to remove the screws and fastens to remove the access panel. You can use a mild detergent and water mixture to clean the coils, simply mix the solution in a spray bottle or garden sprayer and apply it to the coils. Let it sit for a couple of minutes and gently wipe away the debris with a brush or cloth. If you have access to a compressed air unit you can also try to spray the debris off the coil if you don’t want to physically touch them.

Drain Pan

One thing you should check in your HVAC unit is the drip pan. There are usually two different pans in your air conditioning; primary pans and auxiliary pans which hold the water that needs to be drained from your unit. If these pans get full then the stagnant water can develop mold or mildew and cause the smell in your home.

One reason why the pain won’t drain is because it may have rusted and it won’t filter out the water properly. Fortunately, replacing a drain pan (view on Amazon) isn’t a big deal. The first thing you need to do is unscrew the face of your unit and locate the pans inside. First, check to see if the pans are welded, if so you’re going to need a professional to replace them. If not get the model number for your unit and it should be very simple to unscrew or unclasp the pan and replace it with the appropriate part and your AC should hopefully go back to normal.

You Need to Know This About Your AC

If you’re noticing problems with your AC, you need to know what’s causing the issue and if you’ll need to get the AC repaired or replaced. Having a working AC is crucial for any home, and fixing it is just one form of home improvement, but there are many more.

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Bottom Line

After going through these steps make sure you test your AC unit to see if the problem has been fixed. If you’re still having issues it’s best to let a HVAC repairman come take a look.