What is causing the given changes in the DX system where the compressor discharge temperature decreases significantly?

The situation described involves a significant decrease in the compressor discharge temperature of a DX (Direct Expansion) system. When there is an increase in the liquid feed supply to the evaporator, it typically indicates that there is more refrigerant available for evaporation. This heightened availability allows for more efficient heat absorption from the space being cooled.

As the evaporator receives more liquid refrigerant, it can absorb additional heat, enhancing the cooling effect. When the evaporator is performing efficiently, the pressure and temperature of the vapor returning to the compressor can also drop, leading to a decrease in the discharge temperature of the compressor. This is due to the compressor being fed with cooler vapor resulting from the more effective heat exchange in the evaporator.

In this context, the primary driver for the decrease in discharge temperature is the compound effect of increased liquid refrigerant leading to lower vapor temperatures at the compressor inlet. Therefore, the observed decrease in compressor discharge temperature aligns well with the increased liquid feed supply, enhancing the system's overall efficiency.