that part is the suction line to the compressor, its the evaporator outlet, the inlet part is the thinner liquid line. When it reaches the expansion valve - it slows down into a trickle and boils over (soaking the heat from the evaporator).
People mistake this line as "cooling supply line"
btw - txvalve = thermo expansion valve, it regulates the liquid refrigerant and releases it slowly (depressurizing it) which causes it to become a gas (boil over) it sucks the heat from the evaporator making it cold.