🔍 Key Concepts

• Function of a thermal expansion valve (TXV) bulb in sensing temperature and controlling superheat • Relationship between bulb charge and the refrigerant used in the system • Why certain substances (like water or wax) would or would not be suitable in a sealed sensing bulb

💭 Think About

• Think about what the bulb has to do when the suction line temperature changes: how does its internal fluid need to behave? • Consider compatibility: what substance would reliably change pressure with temperature in the same range that the system operates? • Ask yourself which option could practically be used in a small, sealed pressure-sensing device installed on refrigeration piping.

✅ Before You Answer

• Verify what a TXV sensing bulb actually measures (temperature leading to pressure change, not just presence of liquid). • Check the normal operating temperature range of a marine air conditioning system and which of the listed substances behaves predictably in that range. • Eliminate any choice that would be chemically unstable, unsafe, or phase-inappropriate for continuous cycling in a sealed bulb on a refrigerant line.