Different Problems and Troubleshooting of Marine Refrigeration System on Ship

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Marine-Refrigeration-plant

As a Marine Engineer, you may face many problems onboard a ship. The refrigeration system can also get into some trouble from time to time. Some of these problems are common but require immediate attention.

Here are some of the major problems and their troubleshoot in the ship’s refrigeration plant:

Undercharging of Refrigeration System

Indication:

  • The compressor is running hot and the performance of the compressor falls off due to high Superheat temperature at the suction side of the compressor.
  • The suction and discharge pressure of the compressor is low.
  • Large vapor bubbles in the liquid sight glass.
  • Low gauge readings in the condenser.
  • The ammeter reading for the compressor motor is lower than normal.
  • Rise in room temperature which is to be cooled.
  • The compressor is running for an extended period of time.

Causes:

  • Leakage of the refrigerant at the shaft seal, flange couplings, valve gland, etc.
  • The expansion valve may be blocked at the strainer.
  • Partial blockage of the 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.

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 a corresponding increase in the saturation temperature and pressure.
  • The 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 overcharging indications.
  • It may also be due to the formation of ice 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.

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 indications of undercharging. It will contribute to the corrosion in the system. It may cause lubrication problems and the 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.

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 run for an extended period of time.
  • It may cause the gauge pointer of the condenser to jump indefinitely.

Causes:

  • During charging, air may enter the system.
  • If Freon-12 is used air may leaks into 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.

Oil in the Refrigeration System

Indication:

  • Temperature is not dropping in the cold rooms as normal, due to the fact that oil acts as insulation in the evaporator.
  • It may cause excessive frost on the suction line.
  • The refrigerant compressor runs for an extended period of time.
  • The lubricating oil level in the compressor will drop.
  • The refrigerant level will fall if the oil has caused the 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.
  • The compressor may take a high capacity current during starting.

Action:

  • Check the oil separator for proper functioning.
  • Check the drier for proper cleaning and if it requires cleaning clean it
  • The 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 the blow torch.

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.

Evaporator Coil Icing


The icing of the evaporation coils may happen due to:

Cause 1:Too low temperature setting
Action: Increase the coil temperature by adjusting TEV or it’s sensor.

Cause 2: The coil capacity is less
Action: Install large capacity evaporator coils

Cause 3: Defrost is not operational
Action: Check if the defrost system is functioning at regular intervals.

Compressor Start and Stops Frequently

If while maintaining the correct temperature of the ship’s provision room or reefer cargo, the reefer compressor is frequently cutting in and out, then such a problem needs to be sorted out immediately. The most normal causes for such operation are:

Cause 1: Wrong Setting of Cutouts: It may be because the high pressure (HP) cutout is set too high or LP cutout is set too low
Action: Check and change the setting to advisable limit

Cause 2: Differential Setting Span is Small: The low pressure (LP) cut out is provided with starting and stopping pressure setting. If the setting span is too small, it will lead to frequent cut-in and cut-out of the compressor
Action: Change the setting and increase the span between starting and stopping compressor pressures.

Cause 3: Defective Valves: If the compressor discharge valve is leaky or the line solenoid valve is not closing properly, this will
lead to variation in sensor pressure and result in frequent cut-in and cut-out of compressor
Action: Replace all the defective valves

Cause 4: Clogged Suction Filters: The compressor is provided with a filter in the suction line. If that is clogged, it will lead to
frequent LP cut out
Action: clean the filter.

Compressor Starts But Stops immediately.

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

Cause 1: 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.

Cause 2: Defective oil pressure cut out
Action: Check for the proper functioning of the oil pressure cutout and replace the defective cutout.

Cause 3: 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.

Cause 4: 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.

Cause 5: Foaming of oil leading to reduced oil pressure
Action: Ensure no foaming takes place, renew the oil if required.

Cause: Motor overload cutouts are activating
Action: Ensure that electrical motor trips are working properly.

Excessive icing up at Compressor suction:

Causes:

  • Abnormal operation of TEV.
  • Overcharge of the system.
  • Moisture in the system owing to dirty Dryer.
  • Defective Suction valve.

Indication:

  1. Continuous running of Compressor.
  2. Insufficient cooling effects.
  3. Noisy operation.
  4. High suction pressure.
  5. Defective Discharge valve:
    Indication:
  6. Continuous running of Compressor.
  7. Insufficient cooling effects.
  8. Noisy operation.
  9. High suction pressure during running.
  10. Low discharge pressure during running.
  11. Suction pressure rises faster after the Compressor is shut down.
  12. Warm cylinder head.

Choked Expansion valve

Causes:
Due to dirt and freeze-up of water present in the system.
Effects:

  • Starved Evaporator
  • High Superheat temperature.
  • Rapid Condenser pressure rise can cause stopping of Compressor.

  • Remedy:
  • Clean Expansion valve and filter
  • Renew Dehydrator.
DefectCauseRemedy
Compressor starting and stopping too frequently (short cycling)Gas getting trapped in the coil due to over frosting and hence sufficient gas unable to pass through return or suction line causing L.P. cut out.Defrost the coil and collect the gas in the receiver. Once trapped gas is released and coil is defrosted, slowly receiver outlet can be opened and put compressor in use.
Refrigerant charge is lowCharge refrigerant
Air in the system can cause high discharge pressure and cut-off compressor on ‘HP-cut out’.Collect the gas in to receiver and purge out air in the system.
Expansion valve partly blockedClean filters
  
  
  
  
Compressor runs continuouslyRefrigerant charge lowCharge refrigerant
Discharge valves leaking severely.Test the valves. If they leak, overhaul. Otherwise, replace the valves.
Everything alright. During cooling down, compressor works continuously.None. Check all room temperatures and see that they are coming down. Once all temperatures are reached to set value, compressor should stop.
Cooling capacity too small for load.Increase cooling capacity. Increase compressor speed. Check and remove any abnormal heat increments.
Condenser pressure too highAir or non-condensable gases in system. Too much refrigerant in system.Purge receiver and condenser to remove air or non-condensable gases. Drain off excess refrigerant. 
In sufficient cooling water or cooling water temperature too highSupply more or colder cooling water to condenser. 
Dirty condenserClean condenser
Condenser pressure too lowRefrigerant charge is lowCharge refrigerant
Too high cooling water flow or too low cooling water temperature.Reduce cooling water throughput.
Defective piston rings/linerOverhaul piston/liner
Discharge valve malfunctioningOverhaul discharge valve
Suction pressure too highExpansion valve open too much.Adjust expansion valve setting. Check bulb attachment.
Compressor too small in relation to evaporator or load.Increase speed if compressor is running at reduced speed.
Leaky suction & discharge valves. Capacity regulator working.Overhaul suction& discharge valves. Change any worn parts. Check capacity regulator settings.
Suction pressure too lowRefrigerant charge is low.Charge refrigerant
Too much oil circulating in system.Check oil level in compressor. 
Clogged liquid line , expansion valve or dirt retainer.Examine and clean the expansion valve and dirt retainer. 
Compressor too large for cooler.Reduce compressor cooling capacity e.g. by decreasing speed. 
Faulty setting or function of capacity regulator.Inspect and adjust the setting correctly. If required, overhaul the capacity regulator.
Discharge pipe temperature too highRefrigerant charge lowCharge refrigerant
Over load.Reduce load.
In sufficient cooling water or cooling water temperature too highIncrease cooling water flow. Improve condenser efficiency.
Air in the systemPurge air
Dirty condenserClean condenser
Discharge valve malfunctionOverhaul discharge valves
Oil temperature too highOil quality or properties lost due to prolong usage.Renew oil. Use only maker’s recommended oil.
Defective running gears like bearings, piston …Inspect all moving parts and renew if found defective.
Oil in the crankcase disappearsOil separator return valve malfunctioningOverhaul oil separator return valve
Defective piston rings /linerOverhaul piston & liner
Oil in crankcase foamsLiquid in suction lineInspect/ clear TXV
Defective heating element in crankcaseRectify heating element
Oil pressure too lowOil charge is lessCharge oil
Oil collected in oil separator not returning back to crankcase.Clean oil separator and separator return line to crank case.
Worn out or defective bearingsReplace defective bearings
Low air circulationAir flow from chamber room fan is restricted due to fins blocked by frosting.Stop the fan, defrost the coil and fins.
Defective fansIdentify and rectify the defect
Fan motor running in reverse direction due to faultReconnect the electrical connections properly
Compressor noisyVibrations owing to poor bolting or weak foundationsTighten the bolts and strengthen the foundation.
Too much oil in circulation, causing hammering. Liquid hammering owing to Freon liquid accompanying gas into compressor.Check oil level. Expansion valve open too much. Adjust the same.

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