Why is a check valve necessary in the suction line of the lowest temperature coil in a multiple evaporator system?

A check valve is essential in the suction line of the lowest temperature coil in a multiple evaporator system primarily to prevent refrigerant migration. During the off-cycle of the refrigeration system, particularly when the evaporator is not in use, refrigerant can unintentionally migrate back into the suction line or other parts of the system. This can lead to various operational issues, including diminished efficiency and potential flooding of the compressor.

By incorporating a check valve, the system essentially ensures that the refrigerant is directed only in the intended flow direction, preventing it from traveling back towards the evaporators that are not currently active. This is crucial in maintaining the proper function of the entire system, as it helps to avoid issues related to compressor damage, inefficiency, and potential operational failures.

Although enhancing refrigerant flow, eliminating noise, and regulating pressure are all important considerations in refrigeration systems, they do not specifically address the issue of refrigerant migration, which is the primary concern that a check valve mitigates in this scenario.