If the evaporator coil horizontal return line of a container refrigeration system is less than 0.875" (2.21 cm) in diameter (considered small), the thermostatic expansion valve sensing bulb should be attached where on the return line?

Correct Answer: Option B — on the upper surface of the line

Small diameter horizontal return lines require the sensing bulb placed on the upper surface to prevent inaccurate bulb readings caused by liquid refrigerant puddling at the bottom of the pipe.