For proper metering, where should the TXV sensing bulb be mounted?

• A. The receiver outlet
• B. The outlet end of the coil
• C. The suction line near the compressor
• D. The discharge line after the condenser

Answer: (B)

The sensing bulb on a thermostatic expansion valve should be mounted on the suction line at the outlet end of the evaporator coil. This placement lets the bulb sense the actual vapor temperature leaving the evaporator and accurately determine superheat, which is what the TXV uses to meter refrigerant flow. If the bulb were placed on a different part of the system, such as the liquid line after the receiver or on the discharge side after the condenser, it would read the wrong temperature (liquid refrigerant or high-pressure gas), leading to improper metering, unstable superheat, and poor evaporator performance. Mounting on the suction line near the evaporator outlet ensures the valve responds to the true evaporator conditions and maintains proper cooling.