What can cause a refrigeration system to ice up?

Icing up in a refrigeration system is primarily caused by a combination of factors related to air flow, refrigerant levels, and defrosting cycles. Low air flow can lead to insufficient heat exchange, allowing moisture in the air to freeze on evaporator coils. When the refrigerant charge is low, it can also result in a drop in temperature across the evaporator, further promoting ice formation. Additionally, if the defrost cycle is not functioning properly, the system will not effectively remove frost build-up, causing continued accumulation and potentially leading to complete icing.

These combined issues make option B the correct choice, as they directly impact the system's ability to maintain proper operation and temperature control. Other options may touch on different aspects of refrigeration efficiency but do not directly link to icing problems in the same way.