If a system controlled by an ATXV shows high discharge pressure with normal subcooling, what is the most likely cause?

The scenario presented involves an ATXV system that exhibits high discharge pressure while maintaining normal subcooling. The most likely cause of this condition is refrigerant overcharge.

When a system is overcharged with refrigerant, there is more refrigerant than the system can effectively handle. This excess refrigerant leads to increased pressure in the system, particularly in the discharge line, because the compressor is working harder to pump the surplus refrigerant. The high discharge pressure results from the increased volume and pressure of refrigerant being compressed, while normal subcooling suggests that the refrigerant is still condensing appropriately after leaving the condenser, hence it does not indicate any issue with the phase change process at that point.

In comparison, insufficient refrigerant flow, compressor malfunction, and evaporator coil blockage would typically result in different symptoms. Insufficient refrigerant flow would likely cause low discharge pressure, while a compressor malfunction would lead to erratic pressures, not consistent high pressures. An evaporator coil blockage would disrupt the flow through the evaporator, potentially leading to low pressure rather than the high discharge pressure accompanied by normal subcooling. Thus, the condition presented fits best with the context of refrigerant overcharge.