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:
Table of Contents
Undercharging of Refrigeration System
- 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.
- 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.
- 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
- 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.
- 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.
- 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.
- 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
- 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.
- 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.
- 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
- 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.
- 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.
- 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:
- Abnormal operation of TEV.
- Overcharge of the system.
- Moisture in the system owing to dirty Dryer.
- Defective Suction valve.
- Continuous running of Compressor.
- Insufficient cooling effects.
- Noisy operation.
- High suction pressure.
- Defective Discharge valve:
- Continuous running of Compressor.
- Insufficient cooling effects.
- Noisy operation.
- High suction pressure during running.
- Low discharge pressure during running.
- Suction pressure rises faster after the Compressor is shut down.
- Warm cylinder head.
Choked Expansion valve
Due to dirt and freeze-up of water present in the system.
- Starved Evaporator
- High Superheat temperature.
- Rapid Condenser pressure rise can cause stopping of Compressor.
- Clean Expansion valve and filter
- Renew Dehydrator.