Anytime the refrigerant seawater system isn't going to be used for several days, a few extra steps should be taken. For layup, if pumpdown is done by de-energizing a liquid line solenoid valve, the king valve must also be shut for a more positive seal. If there is an isolation valve between the condenser and receiver, this should be shut to isolate the charge in the receiver. The compressor suction service valve should be front seated to isolate the compressor from the chiller. If there is no discharge line check valve, the compressor discharge service valve should also be front seated. Be sure 1/4-inch flare service ports on service valves are securely capped before front seating service valves. In a well designed system, the seawater heat exchangers will drain by themselves when the system is shut down, so no standing water is left in the chiller or the condenser. If the chiller is not self-draining, plugs at the low spots should be removed. The shut-off valve in the condenser water line should be secured and the condenser end plate removed, and its zinc plate checked for action (shell and tube condenser). The end plate can them be bolted loosely into place, to be tighten next time the system is to be operated.
Pencil zincs screwed into water piping and chillers should be renewed regularly. If there is suddenly a notable rise in how quickly they dissolve, the cause is likely an increase in electrolytic action and its source should be located and corrective action taken as soon as possible.