What is a sign that a heat pump TXV device is undercharged?

A sign that a heat pump TXV (Thermal Expansion Valve) device is undercharged is evident through high superheat and low subcooling. High superheat indicates that the refrigerant is too hot as it exits the evaporator, which typically suggests that there is not enough refrigerant to absorb the heat properly. This can lead to overheating of the compressor and reduced efficiency.

On the other hand, low subcooling indicates that the refrigerant is not being adequately cooled after it leaves the condenser, which also suggests an insufficient amount of refrigerant. When the system is undercharged, the balance of heat absorption and rejection becomes disrupted, causing these symptoms. Recognizing these indicators is crucial because an undercharged system can lead to operational issues and potential damage to the heat pump.

In contrast, low superheat and high subcooling would indicate a different issue, likely an overcharged system or a malfunction within the system. Balanced superheat and subcooling would point to a properly charged system, while no superheat would indicate that there is likely liquid refrigerant entering the vapor line, which can be catastrophic for the compressor.