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 A — on the upper surface of the line

On small-diameter suction lines under 0.875 inches, the thermal expansion valve sensing bulb must be mounted on the upper surface (10 to 2 o'clock position). This prevents liquid refrigerant pockets or oil accumulation at the bottom from distorting superheat measurements.