A technician notices one circuit of a multi-circuit evaporator has higher superheat than the others. What could be the likely cause?

The observation that one circuit of a multi-circuit evaporator has higher superheat than the others typically indicates that the refrigerant flow through that specific circuit is restricted. A blocked distributor is a likely cause of this restriction. The distributor is responsible for evenly distributing the refrigerant to all circuits of the evaporator. If it becomes blocked or partially obstructed, it prevents adequate refrigerant flow into that circuit, leading to an increase in superheat as the refrigerant evaporates more fully before reaching the evaporator outlet.

In contrast, a dirty coil would generally affect the overall cooling efficiency, potentially causing low superheat rather than high superheat in one circuit. A refrigerant overcharge typically leads to lower superheat, as excess refrigerant can flood the evaporator, resulting in inadequate heat absorption. Uneven air distribution could create temperature differences across the coil, but again, it wouldn’t specifically result in higher superheat in just one circuit, as the problem would affect multiple circuits rather than isolate to one.

Thus, a blocked distributor clearly explains the situation where one circuit is experiencing higher superheat due to a lack of sufficient refrigerant flow.