5 Reasons Why Your AC Unit Smells Musty

April 2, 2021

When you can smell the air that is coming out of your air conditioning unit, you’ll probably need an experienced HVAC professional to assess your situation. There could be several reasons why your system is omitting a musty odor.

1) Too much moisture in air ducts

High humidity levels or an unnoticed drainage leak can cause excess moisture to accumulate inside air ducts and vents. If you’re smelling something musty when your air conditioner kicks on, there’s a good chance that mold and mildew has spread throughout the ductwork. Mold and mildew can cause upper respiratory problems. You should call a professional ASAP to get your ducts and vents cleaned and repaired so you can eliminate the issue.

2) Frozen Evaporator Coils

Free flowing air is vital for your air conditioner to work. AC units absorb warm indoor air, remove the humidity, cool it and cycle it back indoors through return vents. Any dirt and debris blocking airflow through the filters causes water drops from humidity to form and collect on evaporator coils. Those water drops freeze as the AC unit’s refrigerant cools the air. That’s why changing your filters is so important - they should be cleaned or replaced at least once every month to two months.

3) Full Drain Pan

When the moisture is removed from humid indoor air, it causes water droplets to fall into the drip pain. Since this part of the unit suffers regular wear and tear, it may not function as effectively over time. If not cleaned or replaced, it can accumulate mold, which could cause a musty smell in your vents when the unit is running.

4) Incorrectly Sized AC Unit

If a system is too big for your home, the air gets cycled too quickly, which means it doesn’t have the humidity properly removed. This results in excess moisture. The wrong size unit may also turn on and off constantly, which leads to extra wear and tear and possible failure.

5) Blocked Condensate Line

The small PVC pipe running next to the condenser unit is called the condensate line. It drains water from the drip pan to your landscaping or storm drain. It’s also one of the top locations for mold, mildew, and sludge because it’s so small. This leads to clogs and musty odors in your home. 

If you have any weird smells coming out of your vents when your system runs, you should call a professional. PJ Mac HVAC Service & Repair is here to help!
PJ MAC HVAC Service & Repair
642 Harper Ave.
Drexel Hill, PA 19026
(833) 756-4822
PA Contractor's License # PA157168
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