Purging of air from Refrigeration system

Air can enter refrigeration system while

charging of refrigerant,
charging of oil,
when compressor and other parts are opened for maintenance
or air can also enter if the suction pressure at compressor goes below the atmospheric pressure.

Air in the refrigeration system will manifest itself by increase in discharge pressure as air does not condense in the condenser and the cooling capacity of the system is also reduced.

For removing air from the refrigeration system

the condenser liquid line discharge valve is closed,
the sea water cooling of condenser is kept on and the compressor is run,
all the cold rooms solenoid valves are actuated,
now all the gas from the system gets collected in the condenser,
the compressor runs until it cuts off on low suction pressure.
The collected gas is allowed to settle for a while in the condenser and it all liquefies.
The purge valve on the top of the condenser shell is now opened slightly to purge the air from the condenser.
Purging is stopped when one feels that the refrigerant gas is also now escaping, this will become evident if the escaping gas starts cooling.

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