A thermostatic expansion valve (TEV) that creates an unstable suction pressure is said to be:

A thermostatic expansion valve (TEV) that creates unstable suction pressure is characterized by the term "hunting." This phenomenon occurs when the valve is continually searching for the optimal position to maintain the desired refrigerant flow based on varying conditions such as load changes and evaporator pressure. When a TEV is "hunting," it rapidly opens and closes, which results in fluctuations in the suction pressure. These fluctuations can lead to inefficiencies in the refrigeration system, as they cause the compressor to cycle more frequently than necessary.

The other terms have distinct meanings in refrigerant cycle operations. Flashing refers to the process of liquid refrigerant turning into vapor when it encounters a pressure drop before entering the evaporator, while modulating refers to the valve's ability to adjust flow smoothly rather than in abrupt changes. Fractionating is related to the separation of components in refrigerants and does not pertain to the unstable pressure conditions caused by a TEV. Each of these terms highlights different aspects of refrigeration systems, but in the context of instability in suction pressure, "hunting" is the correct designation for the behavior of the TEV.