HVACR Glossary

Capillary tube
A type of refrigerant metering device. Usually consists of several feet of tubing having a small inside diameter. Selection criteria are based on length and inside diameter. Friction of liquid refrigerant and bubbles of vaporized refrigerant within the tube serve to restrict flow so that correct high- and low-side pressures are maintained while the compressor is operating. A capillary tube refrigerant control allows high- and low-side pressure to balance during the off cycle. Also a small-diameter tubing used to connect temperature control bulbs to control mechanisms.