Marine Engineering Study Materials

There are low pressure and high pressure areas in a refrigeration system. Air can enter in the refrigeration plant when any part of the system pressure drops below atmospheric pressure. If the low pressure (LP) cut off in the plant is malfunctioning or adjusted improperly, there is a chance that the refrigeration compressor keep running even if suction pressure is low and sucking the refrigeration gas into the system. In such conditions, air may enter the the system when pressure in the plant is lower than surrounding air pressure.

Effects of Air in Refrigeration Plant

1. Refrigeration compressor outlet temperature high
2. Condenser outlet temperature high
3. Condenser discharge pressure high
4. Presence of small bubbles in the sight glass
5. Jerking pointer gauge

Remedies for Air in Refrigeration Plan

Follow the procedure below to remove air from the refrigeration system.

1. Change over the compressor to manual mode
2. Now close the liquid stop valve after the condenser
3. Pump the entire gas into the condenser by running compressor
4. Stop the compressor when the suction pressure is just above zero
5. Close the suction valve for compressor
6. Allow the refrigerant to cool down inside the condenser
7. Bleed air slowly by opening purging valve on condenser

Why Refrigeration Compressor Takes Suction from Crankcase

Unlike air compressors, it is common in reciprocating type refrigeration compressors to take suction from crankcase. Outlet from the evaporator coils is led to the compressor crankcase. There are a few advantages with this design.

1. Since crankcase is pressurized, no air can enter the system.
2. No refrigerant gas is wasted by even small blow pasts from the compressor pistons.
3. Refrigerant gas is miscible with oil. This property helps the gas to bring the oil in the system back to the compressor. In some designs, oil in the refrigerant gas drips inside the crankcase before leading it for compression.

See Also: Refrigeration System

See Also: Properties of Refrigerants

See Also: Reheat Air Conditioning System

See Also: Double Duct Air Conditioning System

See Also: Zone Control Air Conditioning System