Orifice Tube

📖 YOUCANIC Automotive Glossary

The orifice tube is a fixed-restriction metering device used in some A/C systems (primarily GM, Ford, and some Asian vehicles) as an alternative to the expansion valve. It is a small tube with a precisely sized orifice (restriction) and a fine mesh screen at each end, installed in the liquid line at the evaporator inlet. Unlike the TXV which varies its opening based on superheat, the orifice tube has no moving parts and provides a fixed restriction — refrigerant flow rate varies only with the pressure differential across it. Systems using an orifice tube use an accumulator (instead of a receiver-drier) on the low-pressure side to catch any liquid refrigerant that passes through the evaporator, preventing it from reaching the compressor.

Orifice tube systems rely on the compressor cycling on and off (controlled by the low-pressure cycling switch) to regulate evaporator temperature, rather than continuous compressor operation with variable metering as in TXV systems. Common orifice tube problems include clogging from debris or system contamination (causing poor cooling and very low low-side pressure), and screen deterioration that allows debris to pass through into the evaporator. The orifice tube is inexpensive and should always be replaced during any A/C system repair that requires refrigerant recovery. Its mesh screens often reveal the cause of A/C contamination — black particles indicate compressor failure, green particles indicate corrosion, and metallic particles indicate bearing wear.