A refrigeration system has a hand-operated needle valve for the refrigerant expansion device. If refrigeration load and suction pressure remain constant, a decrease in condensing temperature will:

• A. Be automatically compensated for
• B. Result in reduced refrigerant flow unless the valve is opened
• C. Increase available pressure difference
• D. Result in greater refrigerant flow

Answer: (B)

The key idea is how the expansion device gets its driving force. Flow through a hand-operated needle valve depends on the pressure difference between the high-pressure side (condenser) and the low-pressure side (evaporator), plus how open the valve is. If the condensing (high-side) temperature falls while the suction pressure stays the same, the high-side pressure drops. That reduces the pressure difference across the valve. With a fixed valve setting, this smaller driving force means less refrigerant can flow through the valve. Since the load and suction conditions aren’t changing, the system won’t automatically increase flow—you’d need to open the valve more to allow more refrigerant to pass. So, refrigerant flow will be reduced unless the valve is opened.