This article addresses two common causes for a foul odour emitting from the air con:
After a period of usage, the air conditioner gathers foul smelling waste product (in the form of mould, slime and mildew) from moisture accumulation when the aircon dehumidifies and absorbs heat from its environment.
Also, air conditioning units with the external section situated outside the home or office will encounter foreign debris being trapped in the aircon duct. When these particles decompose, they cause an unpleasant smell.
Secondly, the standing water in the drip pan may also cause an unpleasant smell to emit from the aircon. Situated on the underside of the aircon, the pan accumulates condensation from the evaporator coil. This pan of stale water may breed mildew and bacteria, which causes a foul smell in the aircon.
To remedy the foul smell produced by the aircon, a professional aircon company will perform a general aircon service for general cases. However a thorough chemical overhaul is needed is the condition that is very bad.