What is a common problem found with water-cooled coils?

A common problem found with water-cooled coils is related to the lack of a backflow preventer. In HVAC systems where water is used for cooling, a backflow preventer is essential to prevent contaminated water from flowing back into the fresh water supply. If a backflow preventer is absent, there is a risk of cross-contamination, which can compromise the safety and efficiency of the system. This issue can lead to various complications, including poor water quality and increased system maintenance needs.

While the other options present possible concerns within HVAC systems, they are not as directly linked to the specific functioning and prevention aspects of water-cooled coils as the absence of a backflow preventer. Overheating, rattling noises, and excessive freezing may indicate operational or maintenance issues in various HVAC components, but they do not specifically address the critical need for a backflow prevention mechanism in water-cooled systems.