Which component connects to the middle port on a gauge manifold?

The middle port on a gauge manifold is specifically designed to connect to a vacuum pump. This is significant because the vacuum pump is an essential tool used in HVAC and refrigeration to remove moisture and air from the system before charging it with refrigerant. By connecting the vacuum pump to the middle port, the technician can create a vacuum that ensures the system is free of contaminants, which is crucial for optimal performance and longevity of the equipment.

In contrast, the other components mentioned, such as the refrigerant cylinder, compressor outlet, and expansion valve, serve different roles and connect to different ports on the manifold. For instance, the refrigerant cylinder connects to one of the designated low or high-pressure ports depending on whether the system is being charged or recovered, while the compressor outlet plays a part in moving refrigerant within the system rather than in the vacuuming process. The expansion valve regulates the flow of refrigerant into the evaporator, thus also not fitting the function associated with the middle port. Understanding these specific roles is important for proper HVAC maintenance and repair practices.