Why would a medium temperature case, such as one at 35°F, need to defrost?

A medium temperature case, such as one operating around 35°F, may need to defrost primarily because the coil temperature can operate below freezing at certain conditions. When there is a buildup of frost on the evaporator coils, it acts as an insulating layer that reduces the efficiency of heat transfer. This can occur even if the medium temperature case itself is set to a temperature above freezing.

In refrigeration systems, if the evaporator coils get excessively cold, condensation can form and freeze, leading to frost buildup. This frost accumulation can impede airflow across the coils and reduce the system's efficiency, eventually requiring a defrost cycle to remove the frost and restore optimal operation.

While frost can occur at temperatures above freezing due to humidity and other environmental factors, the need to defrost is directly tied to the coil temperature occasionally dipping below freezing, causing frost build-up that needs management for continued efficiency and proper operation.