If your A/C unit emits a sewer-like smell only when expelling hot air outside, it is possible that there is a problem with the condensate drain line or the evaporator coil. Here are a few reasons why this issue might occur:
Clogged Condensate Drain Line: The condensate drain line carries moisture and condensation away from the A/C unit. If the line becomes clogged with dirt, debris, or mold, it can create a foul smell. As hot air is expelled, the odor may become more noticeable. Cleaning or unclogging the drain line is usually necessary to resolve this issue.
Mold or Mildew on the Evaporator Coil: The evaporator coil cools and dehumidifies the air before it is circulated back into your space. If moisture accumulates on the coil and is not properly drained or if the coil itself is dirty, mold or mildew can develop. When the hot air passes over the coil, it may pick up the unpleasant odor and carry it outside. Cleaning the coil and treating it to prevent mold growth is typically required.
Decomposing Animal or Organic Matter: In some cases, small animals, birds, or organic matter may have found their way into the A/C unit or near the condenser unit. Over time, if not removed, these substances can decompose, resulting in a foul smell. This smell may become more noticeable when the hot air is expelled. Cleaning the unit and ensuring there are no obstructions is essential in such cases.
Sewer Gas Leak: Although less common, there is a possibility of a sewer gas leak in the vicinity of the A/C unit. If there is a broken sewer pipe or a plumbing issue nearby, the smell of sewer gas can be drawn into the A/C unit and released outside when the hot air is expelled. If you suspect a sewer gas leak, it is important to contact a plumber to address the issue promptly.
To identify and address the exact cause of the sewer-like smell, it is recommended to have a professional HVAC technician inspect your A/C unit. They will be able to diagnose the problem accurately and perform the necessary cleaning, repairs, or maintenance to eliminate the odor and ensure the proper functioning of your A/C system.