If an A/C unit emits a sewer-like smell outside when expelling hot air, it could be due to a few potential causes, and one of them might be related to the coils. Here are some possible reasons:
Clogged Condensate Drain: The condensate drain line is responsible for removing excess moisture that is extracted from the indoor air during the cooling process. If this drain line becomes clogged with algae, mold, or debris, it can create standing water, leading to foul odors. The smell may become more noticeable when the A/C unit expels hot air outside because the warm air can carry the odor more effectively.
Mold or Mildew on Coils: Over time, mold and mildew can accumulate on the evaporator coils due to the presence of moisture and organic matter. When the A/C unit operates, the warm air passing over these coils can carry the smell of mold or mildew outside.
Decomposing Animals or Organic Matter: Sometimes, small animals or debris can get trapped inside the A/C unit or in the vicinity of the outdoor unit. If something decomposes near the unit, it can cause unpleasant odors to be expelled when the A/C is running and blowing hot air outside.
Improper Installation or Maintenance: If the A/C unit is not installed correctly or lacks regular maintenance, it may not drain or vent properly, leading to stagnant water or odors in the system.
To address the issue, it's recommended to contact a professional HVAC technician to inspect the A/C unit thoroughly. They can check the condensate drain line, clean the coils, and identify any potential sources of the odor. Regular maintenance of your A/C system can help prevent these issues and ensure efficient and odor-free operation. If the smell is related to a decomposing animal or other external factors, the technician can help locate and remove the source of the odor.