What is a probable cause for a high temperature differential across the evaporator of an air conditioner?

A high temperature differential across the evaporator of an air conditioner suggests that the evaporator is not absorbing heat effectively, which can lead to poor cooling performance. When the air filter or the evaporator coil is dirty, it restricts airflow. This reduced airflow means that less warm air is passing over the evaporator coil, leading to a lower temperature on the plates, while the temperature of the refrigerant remains relatively high, resulting in a greater differential.

This scenario creates a situation where the evaporation process is less efficient. Therefore, addressing restricted airflow due to dirt and debris build-up on the filter or evaporator will help improve system efficiency and reduce the temperature differential.

In the context of the other options, too much charge could cause flooding of the evaporator but would not specifically cause a high temperature differential. A clogged expansion valve would generally affect refrigerant flow and cooling efficiency but may not directly relate to an increased temperature differential. A dirty condenser coil typically affects the heat rejection process, not the temperature differential across the evaporator.