In a heat pump line set during a cooling cycle, which tube is the suction line?

In a heat pump line set during a cooling cycle, the suction line is typically represented by the smaller diameter tube. This designation is based on the function of the two lines in the system. The suction line carries low-pressure refrigerant gas returning to the compressor from the evaporator coil; hence, it is designed with a smaller diameter to accommodate the lower pressures and higher velocities of the gas.

Conversely, the larger diameter tube is known as the discharge line, which transports the high-pressure refrigerant vapor from the compressor to the condenser, where it is cooled and condensed back into a liquid. Because the discharge line handles higher pressures, it requires a larger diameter to allow for proper flow without excessive back pressure.

Understanding the roles of the suction and discharge lines is critical for servicing heat pump systems, as it affects both the efficiency and functionality of the system during different cycles.