Final answer:
The correct shutdown procedure for a weekend or less is to close the manual steam or hot water supply valve. This stops the flow of heat to a non-operating refrigerator system, which works by transferring heat from inside to outside, conforming to the conservation of energy principle.
Step-by-step explanation:
When shutting down the refrigeration system for a weekend or less, the correct procedure is c) close the manual steam or hot water supply valve. This action will stop the flow of heat to the system, which is crucial when the refrigeration is not in operation. It ensures that the system does not receive unnecessary heating, which could affect the refrigerant and associated components. Draining the cooling water or servicing the purge pump are more relevant for longer shutdowns or maintenance, turning off the air supply to the pneumatic control system may not be directly related to the refrigeration cycle, and opening all disconnect switches would be a complete power shutdown which is not typically necessary for a short period.
Inside a refrigerator or freezer, when the door is closed, the refrigeration cycle functions to transfer heat from the inside to the outside, maintaining the cold temperature within. The refrigerant absorbs heat at the evaporator as it vaporizes and then compresses, discharging heat at the condenser. This process involves work provided by the compressor and adheres to the conservation of energy, as energy cannot be destroyed but converted from one form to another. During this time, the refrigerator works continuously to remove heat from the interior space.