Faults we find in shipboard refrigeration system

1. Undercharging of refrigeration system

     Indication :
  • Temperature of running compressor is high and compressor performance will be low due to high superheat temperature at the suction side of compressor.
  • Low in Suction and discharge pressure of the compressor.
  • In the liquid sight glass we can see large vapour bubbles.
  • Gauge reading is low in the condenser.
  • Compressor motor ammeter reading  is lower than normal.
  • Rise in room temperature which is to be cooled.
  • Compressor is running for extended period of time.
    Causes :
  • Leakage of refrigerant at the shaft seal, flange couplings, valve gland etc.
  • Expansion valve may be blocked at the strainer.
  • Partial blockage of refrigerant at the filter or drier or evaporator may cause undercharging.
    Action :
  • Identify and rectify the leakage of refrigerant from the system.
  • Clean the filter and drier.
  • Charge the system with fresh refrigerant as required.
2. Overcharge of refrigeration system

     Indication :
  • The liquid level in the condenser is too high (high condenser gauge reading). This will reduce the available condensing surface, with corresponding increase in the saturation temperature and pressure.
  • High pressure switch of the refrigerant compressor activates and stops the compressor. • The suction and the discharge pressures are high.

 Causes:
  • It may be due to the reason that excessive refrigerant has been charged in the system.
  • Air in the system may also cause over charging indication. . It may also be due to the formation office on the regulator.
 Action:
  • Remove the refrigerant from the system. This is done by connecting a cylinder to the liquid line charging valve, starting the compressor, and then operating the charging valve.
  • Purge the air from the system and maintain effective cooling. • Remove ice from the regulator by using any of the defrosting methods
3. Moisture in the System

This normally comes with the ingress of air in the system. Moisture may freeze at the expansion valve, giving some of the indication of under charging, It will contribute to the corrosion in the system. It may cause lubrication problems and breakdown of the lubricating oil in the refrigerant compressor.

Action:
  • Renew silica gel in case of minor moisture.
  • Collect refrigerant and remove all air and moisture by vacuum pump if the amount is huge.

4. Air in the System

    Indication:
  • This may cause the refrigeration compressor to overheat, with a high discharge pressure and normal condensing temperature.
  • There are possibilities of small air bubbles in the liquid sight glass of the condenser.
  • Condensing pressure of the refrigerant in the condenser may be high.
  • If there is excessive air, it may reduce the cooling capacity of the system, making the compressor to run for the extended period of time.
  • It may cause the gauge pointer of the condenser to jump indefinitely
  Causes:
  • During charging, air may enter in to the system.
  • If Freon-12 is used air may leaks in to the suction line because the working pressure of the Freon-12 refrigerant is less than the atmospheric pressure.
Action:
  • Air in the system can be removed by collecting the system gas in the condenser, leaving the condenser cooling water on and venting out the air from the top of the condenser because air will not be condensed in the condenser but remains on top of the condenser above the liquid refrigerant.
  • Connect the collecting cylinder to the purging line of the condenser, open the valve, and collect air in the cylinder.
  • After purging the air from the system don't forget to shut the purging valve.
  • Check the level of the refrigerant in the system. If required, charge the system with fresh refrigerant.
  • Restart the compressor with all safety precautions.

5. Oil in the Refrigeration System

   Indication:
  • Temperature is not dropping in the cold rooms as normal, due to fact that oil act as insulation in the evaporator.
  • It may cause excessive frost on the suction line.
  • Refrigerant compressor runs for the extended period of time.
  • Lubricating oil level in the compressor will drop.
  • Refrigerant level will fall if oil has caused blockage.
 Causes:
  • This may happen if the oil separator is not working properly.
  • Oil may carry over from the compressor and may not come back to the compressor due to blockage in the system,
  • Defective piston rings or worn out liner of the compressor may cause the oil to carry over along with the refrigerant.
  • Compressor may take high capacity current during starting
  Action:

  • Check the oil separator for proper functioning.
  • Check the driver for proper cleaning and If it require cleaning clean it.
  • Evaporator coil should be drained to remove any trace of oil.
  • If there is oil in the cooling coils, increase the condenser and evaporator temperature differentials and remove excess frost on the suction pipe.
  • Heat pipes with blow torch.

6. Flooding of Refrigerant in the System

This is seen as liquid getting back to the suction of the refrigerant compressor. It may be due to a faulty or Incorrectly adjusted expansion valve and also due to solenoid valve leakage. It may also result from overcharging of the refrigeration system. Flooding may lead to an iced up evaporator.

7. Evaporator Coil Icing:

Icing of the evaporation coils which may happen due to:

    1. Cause: Too low temperature setting

        Action: Increase the coil temperature by adjusting TEV or it's sensor.

    2. Cause: The coil capacity is less

        Action: Install large capacity evaporator coils.

    3. Cause: Defrost is not operational

        Action: Check if the defrost system is functioning at regular intervals.

    4. Cause: Fresh stock taken to room

    5. Action: Additional defrosting

9. Compressor Starts But Stops immediately

When the compressor in the reefer circuit starts and suddenly stops, it can be because of the following reasons:

1. Cause: Low pressure cut out gets activated

    Action: Ensure that all the suction line valves are in open condition, the refrigeration is properly                          charged and the low pressure cut out is not defective.

2. Cause: Defective oil pressure cut out.

    Action: Check for proper functioning of oil pressure cutout and replace the defective cutout.

3. Cause: Defrosting timer is getting activated frequently

    Action: If the defrost timer is getting activated frequently, leading to cutout of compressor, check                         and repair defrost timer.

4. Cause: The lube oil level is below required level.

    Action: This can be because of leakage of lube oil from seal or carry over of oil. Rectify the leakage                    and refill the oil level. 
5. Cause: Foaming of oil leading to reduced oil pressure.

    Action: Ensure no foaming takes place, renew the oil if required. 6. Cause: Motor overload cutouts                     are activating
6. Cause: Motor overload cutouts are activating.

    Action: Ensure that electrical motor trips are working properly,

10. Excessive icing up at Compressor suction:

Causes:

1. Abnormal operation of TEV.

2. Overcharge of the system.

3. Moisture in the system owing to dirty Dryer.

4. Defective Suction valve:

Indication:

1. Continuous running of Compressor.

2. Insufficient cooling effects.

3. Noisy operation.

4. High suction pressure.

11. Defective Discharge valve:

Indication:

1. Continuous running of Compressor.

2. Insufficient cooling effects.

3. Noisy operation.

4. High suction pressure during running.

5. Low discharge pressure during running.

6. Suction pressure rises faster after Compressor is shut-down.

7. Warm cylinder head.

Choked Expansion valve:

Causes:

Due to dirt and freeze-up of water present in system.

Effects:

1. Starved Evaporator

2. High superheat temperature.

3. Rapid Condenser pressure rise can cause stopping of Compressor,








2 comments:

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