AC blowing sewage smell in evenings: cost to fix?« Back to Previous Page

A sewage smell from an AC, especially one that appears on a schedule, is a common issue in Dubai's climate and typically points to one of two problems. The most frequent culprit is a dry drain line or trap. AC units remove humidity from the air, and the condensate drain line should always hold a little water to block sewer gases from entering your home. In the extreme heat, this water can evaporate, breaking the seal and allowing odours to back up into the system, often becoming more noticeable when the unit cycles on in the evening.

The second, more serious possibility is a cracked or disconnected sewer vent pipe near the AC's fresh air intake. A negative pressure build-up in the drainage system at night, potentially from neighbours' usage, could be forcing those gases into your AC unit.

Changing filters won't resolve either issue. A proper diagnosis requires a technician to inspect the condensate drain pan and trap for blockages or dryness and to test the drain line's seal. They may need to pour water into the trap to re-establish the barrier. For a suspected plumbing issue, they would need to locate the AC's intake and check for proximity to any plumbing vents.

The cost for diagnosis and a simple fix like clearing and priming a drain line is typically on the lower end of service calls. However, if the issue involves accessing and repairing plumbing lines or sealing ductwork, the complexity and cost increase significantly. Always request a detailed assessment and quote before any work begins. For persistent biological odours, a microbial swab of the drain pan can identify if mould or bacterial growth is contributing to the problem.