What refrigerant, when present in excess, causes a reduction in discharge superheat?

Contrary to insufficient refrigerant, when the system is overcharged or the throttling device supplies too much fluid, the liquid refrigerant in the evaporator cannot completely evaporate. A large amount of unvaporized liquid occupies the heat exchange space in the evaporator, which not only reduces heat exchange efficiency but may also enter the suction line along with the airflow.

These residual liquid refrigerants continue to evaporate in the suction line, absorbing heat from the pipe wall and the surrounding environment, thereby cooling the refrigerant vapor in the suction line. As a result, the temperature of the gas entering the compressor is lower than normal, the suction superheat decreases significantly, and even a "wet stroke" (i.e., return gas with liquid droplets) may occur.

Due to the low suction temperature, even after compression, the discharge temperature cannot reach the normal level, so the discharge superheat decreases accordingly. In addition, this state may also pose the following risks: Liquid slugging: Liquid refrigerant directly enters the compressor cylinder, causing mechanical impact due to its incompressibility, which can severely damage valve plates, pistons, or motors; Reduced compressor efficiency: Low-temperature and low-pressure suction reduces the work capacity of refrigerant per unit mass, lowering the overall energy efficiency of the system; Poor lubrication: Excess liquid refrigerant may dilute the lubricating oil, affecting the internal lubrication of the compressor and exacerbating wear.