A typical shipboard domestic multi-box refrigeration system operates with one compressor and condenser. What is the purpose of the sensing line connected to the thermal bulb at the evaporator coil outlet?

Correct Answer: Option D — To transmit the bulb pressure (proportional to the coil temperature) to the thermal expansion valve diaphragm.

The capillary tube and sensing bulb transmit vapor pressure proportional to the evaporator tail coil temperature to the upper side of the thermostatic expansion valve diaphragm, providing automatic superheat control.