All of the following are components of a secondary refrigeration system except ______?

• A. Diffuser
• B. Cooling coils
• C. Expansion tank
• D. Receiver

Answer: (D)

In a secondary refrigeration system, cooling is carried through a secondary fluid (like glycol or brine) that circulates to heat exchangers such as cooling coils to remove heat from the space. The expansion tank is included to accommodate the liquid’s volume changes as temperature varies, preventing pump cavitation and maintaining stable pressure in the secondary loop. A diffuser can be part of the system as a means to distribute conditioned air or the secondary fluid more evenly after it exchanges heat, depending on the air-handling setup. The receiver, however, sits in the primary refrigerant circuit and serves as a storage/settling vessel for liquid refrigerant before it heads to the metering device. It is not part of the secondary loop, so it’s the component that does not belong in a secondary refrigeration system.