When the TEV or a capillary tube is used, a low refrigerant charge will cause which condition?

When a low refrigerant charge is present in a system utilizing a Thermal Expansion Valve (TEV) or a capillary tube, it leads to low head pressure. This phenomenon occurs because the refrigerant is responsible for creating the pressure necessary to circulate through the system. With insufficient refrigerant, the system cannot maintain adequate pressure levels, particularly on the discharge side of the compressor.

Low head pressure is a concern since it can result in inadequate refrigerant flow to the evaporator, which impacts the overall refrigeration cycle. It can lead to reduced efficiency, cooling capacity, and potentially result in compressor overheating due to the reduced ability to reject heat. The other conditions mentioned, such as high evaporator temperature, normal compressor operation, or increased moisture in the system, do not directly reflect the impact of insufficient refrigerant charge in the same way as low head pressure does.