The sensing bulb on a TXV measures which parameter?

The sensing bulb on a TXV measures which parameter?

• A. Ambient humidity
• B. Outlet evaporator temperature
• C. Discharge temperature
• D. Suction line pressure

Answer: (B)

The sensing bulb on a TXV is wired to monitor the temperature of the refrigerant at the evaporator outlet. This location directly reflects how much heat is being absorbed in the evaporator and helps the valve maintain the desired superheat. Inside the bulb is a temperature-sensitive liquid; when the evaporator outlet temperature rises, the liquid expands and increases the pressure in the bulb and capillary line, causing the valve to tighten and reduce refrigerant flow. When the outlet is cooler, the bulb pressure falls, the valve opens more, and more refrigerant flows in. This mechanism keeps the evaporator from being overfed or underfed and protects the compressor by avoiding liquid return. Ambient humidity isn’t what the bulb senses, discharge temperature isn’t the measured parameter, and suction line pressure isn’t directly measured by the bulb—the temperature at the evaporator outlet is the key signal.

The sensing bulb on a TXV is wired to monitor the temperature of the refrigerant at the evaporator outlet. This location directly reflects how much heat is being absorbed in the evaporator and helps the valve maintain the desired superheat. Inside the bulb is a temperature-sensitive liquid; when the evaporator outlet temperature rises, the liquid expands and increases the pressure in the bulb and capillary line, causing the valve to tighten and reduce refrigerant flow. When the outlet is cooler, the bulb pressure falls, the valve opens more, and more refrigerant flows in. This mechanism keeps the evaporator from being overfed or underfed and protects the compressor by avoiding liquid return. Ambient humidity isn’t what the bulb senses, discharge temperature isn’t the measured parameter, and suction line pressure isn’t directly measured by the bulb—the temperature at the evaporator outlet is the key signal.