Which of the following can be a symptom of a faulty air conditioning system?

A symptom of a faulty air conditioning system is the presence of unusual cabin odors. When the air conditioning system is not functioning properly, it can lead to the accumulation of mold and mildew within the system or around the condensing unit. This typically occurs if the system is not effectively draining moisture, allowing for damp conditions where these growths can thrive. As the air circulates through the cabin, it carries these odors into the passenger compartment, creating an unpleasant experience for occupants. Addressing these odors often involves cleaning the system, replacing the cabin air filter, and ensuring proper drainage to prevent moisture buildup.

Other symptoms listed, such as poor fuel economy, reduced acceleration, or increased engine noise, are not directly correlated with the air conditioning system's function and are often indicative of other mechanical issues unrelated to the AC system. For instance, poor fuel economy can be linked to engine efficiency rather than AC performance.