If the TD of an evaporator coil should be 15 ° and you measure only 5 °, what could be the issue if other pressures check out?

If the temperature difference (TD) across an evaporator coil is significantly lower than what is expected, it indicates that the coil is not effectively removing the desired amount of heat from the air passing over it. In this case, the measured TD is only 5 ° while the target is 15 °, pointing to a potential issue with the capacity of the coil.

The high humidity level option suggests that excessive moisture in the air can affect the coil's performance. In high humidity environments, the evaporator coil may struggle to lower the temperature effectively because it is working to condense moisture as well as cool the air. This added burden can lead to a reduced temperature difference. When the humidity is high, the air requires more energy to remove moisture, which can detract from the coil’s ability to reach the desired cooling effect. Hence, the lower measured TD might be indicative of this humidity challenge.

Understanding the specific conditions of the system, including the humidity levels, is crucial in diagnosing cooling issues, particularly when other performance metrics, such as pressure, are within acceptable ranges. Addressing and managing humidity can enhance the evaporator coil's efficiency and help achieve the desired temperature difference.