Which of the following is a possible cause of underfeeding the TEV?

• A. Restricted filter drier
• B. High superheat adjustment
• C. Dead thermostatic bulb charge
• D. Undersized valve

Answer: (D)

The amount of refrigerant that reaches the evaporator is controlled by the size and opening of the thermostatic expansion valve. If the valve is undersized, its maximum flow is limited, so it cannot pass enough refrigerant to meet the evaporator’s load, resulting in underfeeding. This directly explains why underfeeding TEV occurs—the valve simply can’t deliver the required refrigerant regardless of sensor input.

Other issues may affect flow or the valve response, but they don’t directly cap the valve’s flow capacity in the same way. A restricted filter drier can create a pressure drop, which can Doom the system performance but is not the primary limiting factor for TEV metering. A dead thermostatic bulb charge typically causes the valve to respond improperly and often leads to overfeeding rather than underfeeding. A high superheat adjustment changes the target operating condition and can cause the system to meter more refrigerant, not inherently reduce the maximum flow like an undersized valve does.