Auto A/C Terms - Glossary
Equalizer Line - External Equalizer Tube

An equalizer line is typically part of come conventional thermostatic expansion valves or TXVs. The equalizer line should not be confused with the temperature sensing capillary tube. Very little refrigerant passes through the equalizer, even though the line will usually actually thread into the low side line of the A/C system at the POA valve or suction valve.

The purpose of the equalizer line is to provide a shock absorber type effect on the expansion valve. The temperature sensing capillary tube senses evaporator outlet temperatures, causing the expansion valve or TXV to open or close. In order to moderate the motion of the expansion valve, the equalizer line senses actual evaporator pressure from the outlet of the evaporator.

Note that not all expansion valves include equalizer lines. The typical thermostatic expansion valve will always include the temperature sensing bulb attached by a capillary tube to the top of the valve. The equalizer line will attach to the body of the expansion valve. When replacing expansion valves, understand that expansion valves that are not externally equalized can not be substituted for ones that are.