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

The middle port on a gauge manifold is specifically designated for connecting a vacuum pump. This is crucial for situations where the system needs to be evacuated before charging with refrigerant. When servicing refrigeration or air conditioning systems, using a vacuum pump through the middle port allows the technician to remove any moisture, air, or contaminants from the system, ensuring optimal operation and preventing potential damage due to impurities.

In contrast, the refrigerant cylinder connects to the high side port, which is typically used for introducing refrigerant into the system. The condensing unit and expansion valve are integral components of the refrigeration cycle but do not connect directly to the gauge manifold during maintenance and troubleshooting processes. Understanding the correct use of the middle port for connecting a vacuum pump is essential for effective repairs and service in HVAC systems.