When a TEV or capillary tube is used as a metering device, what does a low refrigerant charge cause?

When a TEV (Thermostatic Expansion Valve) or capillary tube is used as a metering device, a low refrigerant charge leads to low head pressure. The head pressure is essentially the pressure in the system's high side, which is responsible for delivering refrigerant to the system.

A low refrigerant charge means that there is less refrigerant circulating through the system, which can impact the overall pressure levels. In this scenario, the compressor may struggle to maintain adequate pressure because there isn’t enough refrigerant to absorb the heat effectively. The result is typically a drop in head pressure because the system does not have enough refrigerant vapor to produce the necessary pressure in the condenser.

Additionally, a low refrigerant charge often leads to a decrease in the efficiency of the refrigeration cycle, which may further contribute to low head pressures and potentially impact cooling performance, but the primary consequence in this context is the reduction of head pressure itself. Excessive superheat can occur in this situation as well, but that relates to the condition of the evaporator rather than the immediate consequence of low refrigerant affecting head pressure.