Jan 09, 2017
A restricted metering device - thermostatic expansion valve or TXV - can cause a number of symptoms in a system. Here are the ways a TXV can become restricted:
Wax buildup in the valve because the wrong oil was used in the system;
Sludge from the byproducts of a compressor burnout;
Partial TXV orifice freeze-up from excessive moisture in the system;
Foreign material in the orifice;
Oil-logged TXV from refrigerant flooding the compressor;
Too much oil in the system;
TXV is adjusted too far closed;
Manufacturer’s defect in the valve; or
Plugged inlet screen on TXV (see Figure No. 1).
A system with a restricted metering device will display the same symptoms as a system with a liquid-line restriction. This is because the TXV is actually part of the liquid line. The liquid line begins at the outlet of the receiver and includes the filter drier, sight glass, and any other components located between the receiver and TXV. Other components may include solenoid valves, hand valves, and the like.