Nothing can destroy the cool comfort of an air-conditioned home on a hot summer day more than an unpleasant odor. If you notice strange smells that seem to be originating from your air conditioner, then the underlying cause may be anything from a minor maintenance issue to a significant fault. Tracking these odors can help to ensure that your air conditioner remains in prime condition. 

Although there are several potential causes for unpleasant AC odors, you can usually get the bottom of the problem by following a few simple diagnostic steps.

1. Thoroughly Clean Affected Rooms

Just because you notice an odor when your air conditioner is running does not necessarily mean that your AC is the source of the smell. Your HVAC system can move a significant amount of air throughout your home, which can sometimes push scents around a room. If you only notice the smell in one or two places, then you should begin your investigation in those areas.

Start by thoroughly cleaning the rooms, paying particular attention to areas near the vents. Avoid using any sprays or cleaners that may mask the scent, since you'll want to know if cleaning solves the problem. If you can still smell something amiss once you know the room is clean, then it's time to move on to the next step.

2. Check and Replace Your Filter

A clogged air conditioning filter can lead to reduced airflow throughout the system, and may ultimately promote the growth of mold within your ductwork. Old, dirty filters can also transmit odors on their own, leading to foul air that works its way through your ductwork. Fortunately, replacing a filter is a cheap maintenance task that you can tackle on your own.

As a general rule, you should replace any filter that's more than a few months old. You should also replace any filter that appears noticeably dirty or damaged. Use your system for a few days after replacement to determine if the odor is gone.

3. Clean Your Evaporator Coils

Your evaporator coils remove heat from the air in your home, and your air handler then pushes this cold air through your home's ductwork. Dirty evaporator coils can produce a moldy odor that may smell like dirty laundry or old socks. In most cases, you can access the evaporator coils through a panel near the air handler.

The easiest and safest way to clean your evaporator is by using a foaming coil cleaner. You can also use compressed air to blow away loose material (such as dust) that may have built up on the coils.

4. Contact a Professional

If the smell persists even after completing these steps, then you may have a moisture problem in your ductwork or another issue requiring professional assistance. An HVAC technician can diagnose the source of your odor so that bad smells don't ruin the joy of a cool and comfortable home.