Which of the following can cause an evaporator to freeze up?

The situation of an evaporator freezing up is typically associated with issues related to airflow or refrigerant levels, rather than humidity control devices like a by-pass type humidifier.

When examining the choices presented, low refrigerant levels is a key factor that can lead to the freezing of an evaporator coil. When the refrigerant is low, it doesn’t absorb enough heat from the air passing over the coil. This inadequate heat absorption allows the coil temperature to drop, potentially reaching the freezing point of water, which leads to ice formation. Ice buildup can obstruct airflow as well, exacerbating the problem further.

Dirty air filters can contribute to the same issue as they restrict airflow over the evaporator coil. A lack of sufficient airflow prevents the coil from adequately transferring heat, which can also result in freezing. However, these aspects focus more on airflow limitations rather than a humidity control function.

High ambient temperatures generally do not cause the evaporator to freeze; instead, they can overloading the system, leading to its inability to effectively cool the air. The context of the question emphasizes situations directly linked to the cooling cycle and refrigerant dynamics specifically.

Thus, when considering causes for an evaporator to freeze, low refrigerant levels stand out as the most directly