air conditioning unit winter care

air conditioning unit winter care

What Causes A Moldy AC Smell In The Fall?

Lori Harris

The fall can be an unusual time of the year for HVAC equipment. Depending on where you live, the temperature may swing wildly from too warm to too cold, leaving you in a limbo between running your air conditioning and heat. If your home uses thermostats with combined cooling and heating modes, then you may leave them at a single setpoint, but is this the right move?

If you're experiencing a moldy (or "dirty sock") smell in the fall, then it may be a sign that you're running your air conditioner too late into the season. Keep reading to learn how seasonal AC odors can be a sign of improper usage.

The Core Cause of Moldy AC Smells

Unpleasant AC odors typically share the same root cause: a build-up of mold, mildew, or bacteria on your evaporator coils or ductwork. When these smells are persistent, then it can be a sign of an on-going maintenance issue that requires a technician to diagnose. If the smell comes and goes, then it may be a result of how you are using your HVAC system.

It's critical to remember that while mold requires several environmental conditions to grow, there's usually only one ingredient missing in most homes: moisture. Once moisture becomes available, inactive mold spores can quickly take hold and begin to grow. When this happens, it's a surefire recipe for some unpleasant odors from your AC vents.

Why Mold May Be More Common in the Fall

In the summer, your air conditioning system should do an adequate job of removing humidity from the air and preventing any build-up of moisture on the evaporator coils. Mold often only develops in these cases if there's a problem with the system or if the fan is left to run continuously. Fans that run non-stop prevent water from draining from the evaporator, pushing that moisture back into your home.

Things can change if you run both your furnace and air conditioner during the fall, however. Your furnace will not change the absolute humidity of the air in your home, and it may even bring humid air in from outdoors. Unlike in the winter, fall air is usually warm enough to contain a decent amount of moisture. This moisture creates the potential for mold growth.

The Steps You Should Take

If you only smell mold when you first turn on your air conditioner, it may not be a severe problem. Confirm that your filter is clean, and your AC and furnace drain pans are clear. As long as there are no evident issues and the smell quickly vanishes, then your system is likely to be working just fine. Cleaning your evaporator coil may also help to reduce or eliminate the problem.

You should call an HVAC technician for an evaluation if the problem persists, however. Persistent moldy smells can indicate an underlying HVAC issue, and they can reduce your home's air quality and even threaten your health.


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air conditioning unit winter care

The air conditioning unit outside your home needs to be taken care of if you want it to keep you cool for many summers into the future. During the winter, should the unit be covered? Do you really need to do anything to winterize the unit? Our blog will show you several ways for you to protect your air conditioning unit through the winter. You will learn how to build a cover, determine if you need to do any work to it and much more. Hopefully what you learn here will help you to keep your unit running well for many years.