In the previous topics, we have discussed about what care and maintenance should be carried out for each component of a refrigeration plant. All that care/maintenance is given the name as Preventive Maintenance. Because it prevents any problem or fault to appear during the operation of plant and halt its working. But in spite of keeping full preventive maintenance as per the set maintenance schedule, some problem, minor or major, may come at any time during the operation of plant. The minor problems generally have minor causes and remedies, which the operator may himself know and rectify. Hence the operator of refrigeration plant should know about the cause and remedies of some routine problems in plant. However, if the problem is major, such as any tube of evaporator or condenser or refrigeration pipe has punctured or any electric motor or component has burnt or the compressor has gone under heavy wear and tear or any other such miscellaneous problem by which the whole refrigeration plant breakdown, it should be attended by expert maintenance staff.
Here we will discuss some common problems, which appear in day to day working of refrigeration plant, and their possible cause and remedies in brief.
i. Compressor is not starting
1. Fault in electric supply to driving motor
Here we will discuss some common problems, which appear in day to day working of refrigeration plant, and their possible cause and remedies in brief.
i. Compressor is not starting
1. Fault in electric supply to driving motor
- Power may not be available. Check with voltmeter or test lamp.
- Voltage may be very low
- Any wire or electric connection may be burnt
- Any defect in motor starter
- Any one phase in 3-phase supply may be dead
2. Faulty overload cut-out/relay. Check it.
3. Faulty thermostatic switch or temperature controller which may keep the compressor in off position even at higher temperature of cold room due to faulty adjustment or wrong position of its probe. Check and readjust.
4. Faulty H.P./L.P. cutout switch due to faulty adjustment. Readjustment is required.
5. In case the motor is rotating without rotating the compressor, drive belt may be loose or worn out. Replace it.
6. There may be any fault in motor or compressor i.e. either may stuck. Remove the connecting belt and try to rotate both by hand. If any one is stuck, it need repair.
ii. Compressor Runs for too Long or Cooling is Slow
1. There may be excessive cooling load. Check if this is the case.
2. Too much frost may have accumulated on evaporator coil, which is cutting the heat transfer and hence cooling rate. Defrost the evaporator.
3. Thermostatic expansion valve may not work properly and may keep less flow of refrigerant even at full load. It may be either due to wrong placement of feeler bulb or less gas in the bulb. Flow of refrigerant may be judged by looking at sight glass or on the scale of rotameter, if fitted in refrigerant line.
4. The temperature controller or thermostatic switch may be faulty.
3. Faulty thermostatic switch or temperature controller which may keep the compressor in off position even at higher temperature of cold room due to faulty adjustment or wrong position of its probe. Check and readjust.
4. Faulty H.P./L.P. cutout switch due to faulty adjustment. Readjustment is required.
5. In case the motor is rotating without rotating the compressor, drive belt may be loose or worn out. Replace it.
6. There may be any fault in motor or compressor i.e. either may stuck. Remove the connecting belt and try to rotate both by hand. If any one is stuck, it need repair.
ii. Compressor Runs for too Long or Cooling is Slow
1. There may be excessive cooling load. Check if this is the case.
2. Too much frost may have accumulated on evaporator coil, which is cutting the heat transfer and hence cooling rate. Defrost the evaporator.
3. Thermostatic expansion valve may not work properly and may keep less flow of refrigerant even at full load. It may be either due to wrong placement of feeler bulb or less gas in the bulb. Flow of refrigerant may be judged by looking at sight glass or on the scale of rotameter, if fitted in refrigerant line.
4. The temperature controller or thermostatic switch may be faulty.
- It may be set for too low temperature. Recheck.
- The temperature sensing probe is placed at wrong position i.e. in the warmer region. Check it.
- There may be some inside fault in its circuit. Take suitable corrective measures.
5. Poor condensation due to high discharge pressure in the condenser. There may be many reasons for high discharge pressure. Purge the air and non-condensable gas, if any. See if the condenser needs cleaning or de-scaling.
iii. Frequent Starting and Stopping of Compressor
1. Fault in setting of cut-in and cutout temperature in temperature controller. The difference in cut-in and cut-out temperature may be very less. Reset the temperature controller.
2. The probe or bulb of temperature controller/thermostatic switch is placed directly in cold air stream in front of blower. Due to that the temperature at probe decreases at a fast rate thus switching off the compressor before the whole space in cold room comes at designed low temperature. Check and re-position the probe.
3. Due to less suction pressure or less amount of refrigerant vapours at the suction of compressor LP cutout may switch off the compressor. There may be many reasons for low suction pressure, such as
iii. Frequent Starting and Stopping of Compressor
1. Fault in setting of cut-in and cutout temperature in temperature controller. The difference in cut-in and cut-out temperature may be very less. Reset the temperature controller.
2. The probe or bulb of temperature controller/thermostatic switch is placed directly in cold air stream in front of blower. Due to that the temperature at probe decreases at a fast rate thus switching off the compressor before the whole space in cold room comes at designed low temperature. Check and re-position the probe.
3. Due to less suction pressure or less amount of refrigerant vapours at the suction of compressor LP cutout may switch off the compressor. There may be many reasons for low suction pressure, such as
- Less quantity of refrigerant in the system.
- -Inefficient heat transfer in evaporator either due to heavy frost or evaporator surface dirty or excessive amount of oil in evaporator or blower is not working, etc.
- Faulty expansion valve, which does not allow the sufficient flow of refrigerant.
4. Faulty overload relay. Check and repair/replace.
5. High discharge pressure due to ineffective condensation of refrigerant vapours in condenser, which switch off the compressor frequently through H.P. cutout.
There may be many reasons for high discharge pressure as follows:
5. High discharge pressure due to ineffective condensation of refrigerant vapours in condenser, which switch off the compressor frequently through H.P. cutout.
There may be many reasons for high discharge pressure as follows:
- Air in the condenser tubes.
- Too much dirt, scale or sludge has accumulated in the condenser tubes.
- Inefficient supply of cooling air or cooling water
6. Faulty H.P. and L.P. cut-out. Check and re-adjust.
iv. In-sufficient Cooling/Cold Room is Less Cold
1. Excessive cooling load than that is designed.
2. Too much crowding of food containers which may restrict the diffusion of cold air. Arrange suitably the food containers.
3. Faulty setting of temperature in Temperature Controller. Reset it.
4. Frequent starting and stopping of compressor or less running time of compressor due to various reasons explained in the previous section. Take corrective measures.
5. In-efficient refrigerant flow rate due to less charge in the system. Check the correct pressure of refrigerant in the system.
6. In-efficient compressor, which is not compressing the gas efficiently because of heavy wear and tear or loose driving belt. Take necessary action.
7. Condenser becomes ineffective and need cleaning and servicing.
8. Evaporator coil is less effective due to heavy frost or excessive oil in tubes. So,defrost it and drain the oil, if any.
9. Faulty thermostatic control valve, which does not increase the flow rate of refrigerant liquid to evaporator on increase in superheating in evaporator or increase in cooling load. Check the feeler bulb and capillary. Also check for sticky valve.
10. In case of float valve, the valve may stick in the valve seat thus starving the evaporator from liquid refrigerant. Float valve needs servicing.
v. Heavy Cooling/Cold Room is too Cold
1. Fault in temperature controller setting.
iv. In-sufficient Cooling/Cold Room is Less Cold
1. Excessive cooling load than that is designed.
2. Too much crowding of food containers which may restrict the diffusion of cold air. Arrange suitably the food containers.
3. Faulty setting of temperature in Temperature Controller. Reset it.
4. Frequent starting and stopping of compressor or less running time of compressor due to various reasons explained in the previous section. Take corrective measures.
5. In-efficient refrigerant flow rate due to less charge in the system. Check the correct pressure of refrigerant in the system.
6. In-efficient compressor, which is not compressing the gas efficiently because of heavy wear and tear or loose driving belt. Take necessary action.
7. Condenser becomes ineffective and need cleaning and servicing.
8. Evaporator coil is less effective due to heavy frost or excessive oil in tubes. So,defrost it and drain the oil, if any.
9. Faulty thermostatic control valve, which does not increase the flow rate of refrigerant liquid to evaporator on increase in superheating in evaporator or increase in cooling load. Check the feeler bulb and capillary. Also check for sticky valve.
10. In case of float valve, the valve may stick in the valve seat thus starving the evaporator from liquid refrigerant. Float valve needs servicing.
v. Heavy Cooling/Cold Room is too Cold
1. Fault in temperature controller setting.
- Setting of temperature is disturbed and it is set for a lower temperature. Reset it.
- Temperature controller is not working i.e. is not switching off the compressor
when designed temperature is attained. Check and adjust it.
- Temperature sensing probe is placed at some dead zone, which is warmer than the cold room. Place it correctly.
- Faulty probe which is not giving correct temperature. Replace the probe.
vi. Excessive Power Consumption of Refrigeration Plant
1. Due to increase in cooling load by
1. Due to increase in cooling load by
- Increase in temperature of products at the time of storing.
- Surrounding temperature is very high due to hot season.
- Doors of cold room are kept opened for longer times than required.
- Door sealing/ gasket has worn out
- Insulation may become less effective by absorbing moisture from any broken layer
2. In-efficient compressor which need overhauling or replacement.
3. Capacity of condenser is either small or it has become less effective due to other reasons.
4. Capacity of evaporator is small than the designed load or it has become less effective due to other reasons.
5. Quantity of refrigerant is either more or less than that required i.e. suction and discharge pressures are not in designed range.
All the above causes are required to be rectified for reducing the power consumption or running cost of plant.
vii. Noisy Operation
If any part of refrigeration system is producing abnormal noise during running of plant, mostly it itself indicates that what is wrong with it. And so one can judge easily by common sense that what remedial action is required.As the compressor has many moving parts, it can produce different types of abnormal sounds due to any type of wear and tear, which should be checked by some expert maintenance staff.
3. Capacity of condenser is either small or it has become less effective due to other reasons.
4. Capacity of evaporator is small than the designed load or it has become less effective due to other reasons.
5. Quantity of refrigerant is either more or less than that required i.e. suction and discharge pressures are not in designed range.
All the above causes are required to be rectified for reducing the power consumption or running cost of plant.
vii. Noisy Operation
If any part of refrigeration system is producing abnormal noise during running of plant, mostly it itself indicates that what is wrong with it. And so one can judge easily by common sense that what remedial action is required.As the compressor has many moving parts, it can produce different types of abnormal sounds due to any type of wear and tear, which should be checked by some expert maintenance staff.
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