The thermostatic expansion valve are replacing the old capillary tubing. Capillary tube is the less efficiency parts. Nowadays, the higher efficiency central air conditioner units are not using capillary tube.
Capillary tube is another form of metering device or expansion device. The main purpose of the capillary tube is to reduce the pressure from the condenser units. The capillary tubing also determines how much refrigerant the evaporator needs. However, in capillary tube the orifice is fixed.
This is quite confusing! You meant why capillary tube used in refrigeration in a specific term? Or in general term.... Why metering device used in refrigeration?
