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 C — on the upper surface of the line

On small suction lines under 7/8 inch in diameter, the thermostatic expansion valve sensing bulb must be mounted on the upper surface of the horizontal pipe. This ensures accurate bulb temperature sensing without interference from localized oil pools.