An equalizer line is a small-diameter copper tube used with a Thermal Expansion Valve (TXV) to help it sense the actual pressure at the evaporator coil's outlet. This feedback allows the valve to adjust the refrigerant flow much more accurately than a valve without one. By accounting for the pressure drop across the AC Coil Systems, the equalizer line ensures that the coil is always fully utilized without "slugging" the compressor. This is a standard feature in high-capacity Air Handlers and Light Commercial Mini Splits. Proper placement and brazing of this line are critical for the efficiency of your ACIq cooling system. If the line is kinked or poorly connected, the system may struggle to cool or could freeze up entirely. It is a subtle but essential part of the high-precision refrigeration cycle found in modern homes. This line is what allows the TXV to "think" in real-time based on the system's actual load.