In this short podcast episode, Bryan walks through some common thermostatic expansion valve (TXV) troubleshooting scenarios. Many of the same principles apply to troubleshooting electronic expansion valves (EEVs). These dynamic metering devices maintain a constant superheat.
Troubleshooting does NOT start and end with the TXV. First, you need to inspect components (especially filters, ductwork, and filter-driers) and confirm the airflow and charge. You can use measureQuick to monitor superheat, subcooling, static pressure, and other key measurements, and the TrueFlow grid can give you a true idea of the CFM your system is moving. Keep in mind that superheat and subcooling values can vary by system.
Airflow problems and filter-drier restrictions may mimic failed TXV conditions. Ideally, the liquid line filter-drier will be located indoors, and you can check for a pressure drop across it by looking for temperature differentials. You need a full column of liquid going into the filter-drier, and you can use a thermal imaging camera to see the desuperheating, condensing, and subcooling phases inside the condenser coil.
The TXV has a bulb that can be loose, improperly mounted, or improperly insulated; when there is an issue with the bulb, there will likely be low superheat. The bulb should be on a clean and [ideally] horizontal portion of the suction line, and it should be strapped with copper or stainless steel straps. Insulating the bulb is especially important when it's externally located and when low superheat or flood back is a concern.
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