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Topics on Mechanical Engineering Courses

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FILLING BLANKS-REFRIGERATION         Refri controls Filling blanks          Refri Trouble shooting-2           Refri trouble shooting-1

Filling blanks in refrigeration is possible only if one has deep understanding and clarity about the topic. Filling blanks will further increase knowledge which will help to apply in real life applications.


Fill in the blanks in refrigeration is from university question papers

  1. The high pressure is from —————— to ———————–in a refrigeration system.
  2. The condition of refrigerant at the inlet of evaporator is ————–liquid and vapor.
  3. At the outlet of evaporator, the condition of refrigerant  is ——— and —— vapor.
  4. Inlet of the compressor, the condition of refrigerant is ———-pressure and —–temperature vapor.
  5. Refrigerant condition at the outlet of compressor is high————- and high———vapor.
  6. The refrigerant at the inlet of condenser is ————– pressure and ———temperature vapor.
  7. The state of refrigerant at the outlet of condenser is high ———— and high———– liquid.
  8. The condition of refrigerant at the inlet of expansion valve is ——-pressure and ——temperature liquid.
  9. The condition of refrigerant at the inlet of evaporator is ————–liquid and vapor.
  10. The condition of refrigerant at the inlet of evaporator is saturated ———and —– vapor.
  11. The most commonly used Freon R—and R—have been banned,
  12. The most commonly used refrigerant in industry is ———————.
  13. The most commonly used refrigerants in window air conditioner is ————-.
  14. The condenser is the ——–pressure side of a refrigeration system.
  15. The low pressure side starts from ————–expansion valve and ends at ———–of compressor.
  16. The high pressure starts —————- of compressor and ends at the ——————–expansion valve.
  17. The function of the compressor is to increase ————— and —————.
  18. Refrigeration is a process of ——————–.
  19. The process of refrigeration is used to protect —————–against spoilage.
  20. The growth of bacteria is greater in a ————————-atmosphere.
  21. The growth of bacteria can be stopped by ———————.
  22. Refrigeration is based on the principle that ————causes cooling.
  23. Refrigeration capacity is expressed in —————–.
  24. One ton of refrigeration is equal to ——————kJ/day.
  25. One ton of refrigeration is equal to ——————kJ/hour.
  26. The machine which produces refrigeration is called ————————system.
  27. The most popular system for producing refrigeration is ———————-.
  28. The refrigeration system which is equipped with ——————is called a vapor compression refrigeration system.
  29. The system which produces cooling with water is called ————————-.
  30. The temperature decrease in the room due to a desert cooler is ——————–0
  31. ————-energy is used to run the vapor absorption refrigeration system.
  32. In the absorption refrigeration system, the refrigerant is separated from the absorbent in the ——–.
  33. In the absorption system, absorbent absorbs the refrigerant in the —————–.
  34. Mechanical refrigeration system is also called ——————————.
  35. The low pressure of the refrigeration system is also called ——————-, suction pressure and evaporator pressure.
  36. The high pressure of the refrigeration system is also called ——————-, discharge pressure and condensing pressure.
  37. The compressor in the refrigeration system compresses the vapors and increases its —————-and —————.
  38. The oil separator separates the ——————-from the compressed refrigerant.
  39. The condenser is air cooled, water cooled and ———————— cooled.
  40. The condenser changes the vapor refrigerant into a ———————-state.
  41. Receiver is a —————————–tank.
  42. Expansion valve changes high pressure liquid refrigerant into —————liquid.
  43. Accumulator —————–the liquid which comes from the evaporator.
  44. Muffler reduces the suction and discharge —————— of the compressor.
  45. —————pipe is used in the ammonia vapor absorption refrigeration system.
  46. There is no ————–part in the vapor absorption refrigeration system.
  47. Gases which are charged in the Electrolux refrigerator are —————-and —————–.


  1. Compressor, Expansion valve,
  2. Saturated,
  3. Dry, saturated,
  4. low, low
  5. pressure, temperature
  6. high, high
  7. pressure, temperature,
  8. high, high
  9. liquid, saturated,
  10. saturated,
  11. 12 , 11,
  12. Ammonia,
  13. R-22,
  14. high,
  15. middle, inlet
  16. outlet, middle
  17. Pressure temperature,
  18. (Cooling),
  19. (Food stuff),
  20. (Hot and humid),
  21. (Cooling),
  22. (Evaporation),
  23. Tons of refrigeration),
  24. (302400),
  25. (12600),
  26. (refrigeration),
  27. (Vapor compression refrigeration system),
  28. (Compressor),
  29. (Desert cooler),
  30. (100C),
  31. (Heat),
  32. (Generator),
  33. (Absorber),
  34. (Vapor compression refrigeration system),
  35. (Back pressure),
  36. (Head pressure),
  37. (Temperature and pressure),
  38. (Lubricating oil),
  39. (Evaporative),
  40. (Liquid),
  41. (Storage),
  42. (Low pressure),
  43. (Stores),
  44. (sound),
  45. (Steel),
  46. (Moving),
  47. (Ammonia and Hydrogen).




It is used in aircrafts of the entire world. There are different cooling arrangements for the air conditioning of aircrafts. Here boot strap and reduced ambient cooling systems are discussed here.


Boot Strap Air Refrigeration System: Two systems

  1. Without evaporative cooling,
  2. With evaporative cooling





In this, there are two compressors, two heat exchangers and one turbine. Normally second compressor is run by the expansion turbine. In case of evaporative cooling in Boot strap, another water cooled heat exchanger is placed after the second heat exchanger in Fig. above.


Reduced Ambient Air Refrigeration System



It uses two turbines and one compressor. Turbine 1 uses rammed air. The air from turbine 1 enters the heat exchanger. Turbine 2 uses air after the heat ex-changer for further cooling.

Turbine 1 has input and output points as 2 and 4.

Cooled air from turbine 1 enters the first Heat exchanger at point 4.

Heat exchanger has input at points 3 and 5.


Turbine 2 has input and output points as 5 and 6.

Procedure of calculation is similar to the BOOT STRAP SYSTEM.



Summary of air conditioning includes comfort and industrial processes. It increases the comfort to living beings and improve the quality of industrial products.

Definition Of Air Conditioning

It controls simultaneously four parameters, temperature, humidity, purity and velocity of air in a closed space. Further, air conditioning is cooling in summer with ventilation and heating in winter with ventilation.

Practical Applications of summary of air conditioning

  1.  Comfort as well as food preservation need air conditioning
  2. Measuring instruments for more accuracy  and better quality require air conditioning.
  3. Comfort Air Conditioning is of three types, namely, summer air conditioning, winter air conditioning and year round air conditioning.
  4. Human comfort is required in homes, offices and restaurants.
  5. All types of vehicles, namely, cars, buses, trucks, trains and airplanes use air conditioning..
  6. Printing, drugs, rubber and textile industries for controlling conditions to result in more production with better quality need air conditioning.
  7.  Shops, cinemas, hospitals, libraries, computer centers, beauty saloons, malls, telephone exchanges, data processing centers, mines and museums need air conditioning..

 Comfort Conditions for the human beings

Human comfort conditions are temperatures between 22 to 270C with relative humidity between 35 to 60 %, CO2 ≤ 600 ppm,     CO≤ 25 ppm, odorless, virus free, fungus free and air velocity from 0.20 to 1.2 m/s. Purity of conditioned air is maintained with the help of a filter

Types Of Air Conditioning Units

Air conditioning units are window, central and unitary units.

Window units

Window units are used up to 3 ton capacity. Unitary units are from 10 to 50 tons capacity and central air conditioning plants are for a cooling capacity of more than 50 tons. The main refrigerant used is R-22 in window air conditioners and central air conditioning plants. In the unitary units, refrigerant used is R-410 As. Room conditions change to comfortable conditions using various processes of simple cooling, simple heating, heating and humidification, cooling and de-humidification .

Central air conditioning plant

Main components of central air conditioning plants are compressor, condenser, expansion valve, evaporator, fans and blowers, filters louvers and ducts. Air conditioning requires fresh ventilation to maintain requisite level of oxygen in the space being air conditioned.  Air conditioning deals with temperatures above C. Central air conditioning plants use Fan coil units and Air Handling Units. Further, central air conditioning plants are of two types, namely, direct expansion type and chilled water systems. Main supply, main return and branch ducts are used in the central air conditioning system.

Unitary unit

These are factory assembled units having cooling capacity from 10 to 50 tons. In these, condensers are water cooled.

Heating Ventilation Air Conditioning (HVAC)

Year round air conditioning units are called HVAC Units or Complete system of heating, ventilation and air conditioning is called HVAC. This system has become more popular.





This chart contain moist air properties.


Refer Fig. is a Psychrometric chart.


  • Dry bulb temperature is the abscissa (along x-axis) and specific humidity is the ordinate (along y-axis) at 1 atmospheric pressure. It contains the following lines:
  • Vertical lines for dry bulb temperature
  • Horizontal lines towards right for specific humidity
  • Horizontal lines towards left up to saturation curve  for dew point temperature.
  • Relative humidity lines are curves, on the extreme left is 100 % relative humidity line. Then 90 % 80% and so on.
  • Constant enthalpy lines and wet bulb temperatures are slant (diagonal ) lines and coincide.
  • Constant volume lines are also slant lines but are having more slope than the enthalpy lines.
  • Wet bulb temperatures are available on the saturation curve (100 % RH).
  • dew point temperatures are available on the saturation curve (100 % RH
  • Enthalpy lines represent the enthalpy of moist air per kg of dry air.

Psychrometric properties

  1. Dry bulb temperature, tdb
  2. Wet bulb temperature, twb
  3. Dew point temperature, tdp
  4. Specific humidity, w
  5. Relative humidity, Ф
  6. Enthalpy of moist air, h
  7. Specific volume of moist air/kg of dry air

 Utility of the psychrometric chart

When any two of the above properties are known, then the remaining five properties can be determined.

Suppose dry bulb and wet bulb temperatures are given.

Draw a vertical line as per given dry bulb temperature and move along the constant enthalpy line as per given wet bulb temperature. It will meet the dry bulb vertical line. Yhus we get a point on the chart.

(i) To find the dew point temperature, move horizontally towards left till it meets the saturation line.Read the dew point temperature at this point.

(ii) to  find the specific humidity, move horizontally towards right extreme and read the value on the vertical line.

(iii)To find the relative humidity, find the position of the point in between two relative humidity lines and interpolate the required value.

(iv) To find the enthalpy, locate the constant enthalpy line passing through the point. Read its value from the enthalpy values marked on the chart.

(v)To find the specific volume, locate the two specific volume lines in between which the point lies. Interpolate the value of specific volume at the point

Use of psychrometric chart

we can know the condition of air present in a room, varanda outside (covered or uncovered) or anywhere by the use of a sling Psychrometer by measuring the dry and wet bulb temperatures. With the help tdb and twb, first point can be located on the psychrometric chart. We know the condition to be maintained in the conditioned room. Thus another second point can be marked on the Psychrometric chart. Now it is required to reach from first point to second point  in order to make the room air conditioned.This can be achieved with the help of horizontal, vertical lines and moving along the saturated curve. These movements are called psychrometric processes shown in Fig. below.


  • Sensible heating moving horizontally towards right of the point.
  • Sensible cooling moving horizontally towards left of the point.
  • Humidification moving vertically upwards of the point
  • Dehumidification moving vertically downwards of the point
  • Heating and humidification
  • Cooling and dehumidification
  • Cooling and humidification
  • Heating and dehumidification


In this there are two streams. One is room recirculated air while other is the fresh air. These are mixed either before the cooling coil or after the cooling coil.Let the flow rates of recirculated air be = m.1 and of fresh air be = m.2 . Let the mixture condition is point ‘3’.The condition of the mixed air can be found by using the moisture balance and enthalpy balance.

Moisture balance

m.1w1 + m.2w2 = (m.1 + m.2)w3

Energy balance

m.1h1 + m.2h2 = (m.1 + m.2)h3




Psychrometry is the study of the properties of moist air (dry air + water vapor). It includes the study of various temperatures, humidity and Psychrometric processes.

  1. Dry Air

It is a mixture of gases (mainly oxygen and nitrogen) which does not contain water vapor.

  1. Wet air

Wet air or moist air is a mixture of dry air and water vapor.

  1. Saturated air

Saturated air is one which contains maximum water vapors at a particular temperature.

  1. Dry air temperature

Temperature of dry air is the temperature of atmospheric air (moist air). It is measured by an ordinary thermometer.

  1. Wet bulb temperature

Wet bulb temperature is that temperature at which moist air fully saturated. It is measured by a wet bulb thermometer fixed on the Sling Psychrometer.

  1. Sling Psychrometer

6.Dry bulb and wet bulb temperatures can be experimentally measured with a ‘Sling Psychrometer’.

  1. Dew point temperature

Dew point temperature is that temperature at which first condensation of water vapor takes place on cooling the moist air. Normally dry bulb temperature is greater than wet bulb temperature. Wet bulb temperature is greater than dew point temperature.

  1. Saturated air

When the moist air is fully saturated, dry bulb, wet bulb and dew point temperatures are equal. The relative humidity is also 100 %.

  1. Specific humidity 

Specific humidity (w) is the amount of water vapor per kg of dry air. Mathematically

w = 0.622 pwv/(pt–pwv)

  1. Relative humidity

Relative humidity is defined at a particular temperature as the ratio of mass of water vapor per unit volume of moist air to the mass of water vapor when saturated per unit volume. It is expressed as percentage. It is represented by the symbol ‘Ф’. Mathematically

Ф = pv/pvs

Where pv is pressure of water vapors. It can be found from steam tables corresponding to the dry bulb temperature.

pvs is pressure of water vapors when saturated. This can be found from steam tables corresponding to the wet bulb temperature.

  1. Degree of saturation

Degree of saturation is defined at a particular temperature as the ratio of mass of water vapor in per kg the dry air to the mass of water vapor when saturated per kg of dry air. It is represented by the symbol ‘ μ’. It is unit less. It can be as 0.56 etc.

  1. Enthalpy of moist air

Enthalpy of moist air is the sum of enthalpy of dry air and enthalpy of water vapor portion in 1 kg of dry air.

Let w be the mass of water vapor in 1 kg of moist air. Mathematically

Enthalpy of moist air/kg of dry air, hma

hma = 1 cp dt + w [hg +cpv (tdb -tdp)]

FILLING BLANKS-REFRIGERATION COMPONENTS         Refri controls Filling blanks          Refri Trouble shooting-2           Refri trouble shooting-1


Fill in the blanks increases deep understanding as well as knowledge. Especially fill in the blanks in University Question Papers is of utmost importance. 

  1. Oil separator

An oil separator is always placed in the ————-line.

  1. Crank case

A crank case heater is connected in such a way so that it is ———–when the compressor is off.

  1. Compressor

The compressor is called the ————- of the refrigeration unit.

  1. Anemometer

Anemometer is used to measure the ————–.

  1. Dehydrator

Dehydrator is used to remove —————-from the refrigeration system.

  1. Refrigerant Leakage

———–to detect the leakage of Freon refrigerants.

  1. Thermo-couple

Thermo-couple is used to measure —————–.

  1. Ton of refrigeration

One ton of refrigeration is equal to ————–kJ/hour.

  1. Heat rejected in condenser

In a refrigeration system, heat rejected in the condenser is equal to the sum of —————- and———-.

  1. Sensible heat

Temperature difference senses—————-heat.

  1. Refrigerant

Chemical name of R-134a is ————————————.

  1. Horse power

One Horse power in S.I. units is equal to —————Watts.

  1. Running capacitor

Running capacitor is used to improve —————–.

  1. Condenser

Due to poor cooling in the condenser,——————-increases.

  1. Cooling capacity

Cooling capacity decreases with the decrease of————–pressure.

Tons of refrigeration decreases with the increase of —————pressure.

  1. COP

COP increases with the increase of ———————pressure.

  1. Solenoid valve

Solenoid valve is fitted in the —————–line.

  1. Sight glass

Bubbles in the sight glass indicates————–of refrigerant in the refrigeration circuit.

  1. The compressor never stops when there is —————of refrigerant.
    1. Ice

Ice is —————- than water.

  1. Saturated air

In the saturated air, dry bulb temperature, wet bulb temperature and ————-temperature are same.

  1. Boiling point

The normal boiling point of ammonia is ———————0

Water is used as a refrigerant ————— ——-refrigeration.

  1. Specific heat

The highest specific heat is for —————.

  1. Entropy

—————-is constant in a reversible adiabatic process.

  1. Refrigerator capacity

The capacity of a refrigerator is expressed in —————–.

  1. Water cooler capacity

The capacity of a water cooler is expressed in —————–.

The air conditioner capacity is expressed in —————–.

  1. Air refrigerant

Air is used as a refrigerant in the ————————-air conditioning.

  1. Vapor absorption system

There is no ———–part in a vapor absorption system. The gases charged in an absorption system are ————– and ———-. The pressure in the various parts of an absorption system is ——————.

  1. Piping

The material of piping in vapor absorption is—————–.

The material of pipe with R-134a is ———————.

  1. Liquid refrigerant —————-in the evaporator.
    1. Receiver

Receiver is fitted after the —————-unit.

  1. Accumulator

An accumulator is fitted between ————– and ————–.

An accumulator separates ————-and ————.

  1. Muffler

The function of the muffler in a refrigeration system is to reduce ———-.

Cooling in the evaporator is due to ———-heat transfer.

  1. Expansion process

The expansion process is at —————– enthalpy.

The expansion process changes high pressure high temperature liquid into low pressure ——- and ——–.

The expansion valve in small refrigeration unit is a ————————.

ANS: 1.Discharge, 2.on, 3.heart, 4.velocity, 5. Moisture, 6. Halide torch, 7. Temperature, 8. 12600, 9.Cooling effect, work input, 10.sensible, 11. Tetra-fluoro ethane 12. 735.5, 13. Power factor, 14.discharge, 15. Evaporator, discharge 16. Evaporator, 17. Liquid 18. Vapor, 19. Shortage, 20. Excess, 19. Lighter, 20.dew point, 21. –33.50C, Steam jet, 22. Water, 23. Entropy, 24. Tons, 25. Liters, tons, 27.aircraft 27. Moving, ammonia, Hydrogen, same 28. Steel, copper, Evaporates, 29. Condenser, 30. Evaporator, compressor, Liquid, Vapor, 31. Noise, Latent 32.Constant, Liquid, Vapor, Capillary tube


FILLING BLANKS-CONTROLS IN REFRIGERATION        Refri Filling Blanks          Refri Trouble shooting-2           Refri trouble shooting-1           Refri Filling Blanks evaporators



Controls and safety devices in refrigeration are  extremely important to make the operation automatic and safe. Thermostat makes the motor off as soon as the pre-fixed temperature is achieved. Absence  of a thermostat will keep the refrigeration in working unnecessary resulting in the wastage of power without achieving any useful purpose. Safety devices protect the unit from damage. The filling of blanks for controls in refrigeration will increase the understanding as well as practical knowledge.

  1. Thermostat is connected in ——-circuit with the electric motor.
  2. Temperature, which is controlled by a Thermostat is ———of the evaporator.
  3. The feeler bulb of the thermostat is connected at the ———— of the evaporator.
  4. Motor ———at the cut in point of the motor control.
  5. Electric motor ——– at cut out point of the motor control.
  6. The difference between the cut out and cut in point of the motor control is called ——-.
  7. Oil pressure safety control stops the compressor motor at the ——of oil pressure in the compressor sump.
  8. High pressure cut out comes in action as the ———— pressure increases beyond the upper set limit.
  9. Low pressure cut out stops the motor as the—————-pressure decreases below the set limit.
  10. High pressure cut in comes in action as the ———— pressure decreases below the lower set limit.
  11. Low pressure cut in starts the motor as the—————-pressure increases beyond the upper set limit.
  12.  Increase of resistance in a series circuit,  ———— the voltage.
  13. When connected in series circuit, ———— current flows each resistance.
  14.  Number of currents, in a parallel circuit, is equal to the number of ————–in parallel.
  15. In a parallel circuit, voltage across each resistance is ————-.
  16. ————meter is always connected in series in the electrical circuit.
  17. ————meter is always connected in parallel in the electrical circuit.
  18. Fuse is a —————device in the electric circuit.
  19. Humidistat controls the ————–.
  20. Hygrometer is used to measure —– in air.
  21. Hydrometer is used to measure —– of the brine.
  22. Pyrometer is used to measure a very —– temperature.
  23. Anemometer is used to measure ——– of air.
  24. ———–to measure the viscosity of the lubricating oil.
  25. ———–decreases the humidity in the air.
  26. Silica gel in filled in the drier cum filter in order to————-moisture.

ANS: 1.Series 2.  Difference, 3.outlet, 4.Starts,           5.stops,           6.differential, 7. Decrease, 8.discharge, 9.suction, 10.discharge, 11. Suction, 12.decreases, 13.same, 14.resistances, 15.same, 16. Ammeter, 17. Voltmeter, 18. Safety, 19. Humidity, 20.Hygrometer, 21. Hydrometer, 22. Pyrometer, 23. Anemometer, 24.Visco-meter, 25. Dehumidifier, 26.absorb



REFRIGERATION AND AIR CONDITIONING-TROUBLE SHOOTING-2        Refri Filling Blanks         Refri controls Filling blanks           Refri trouble shooting-1           Refri Filling Blanks evaporators





Sr.No. Possible cause Check and remedy
1. Improper refrigeration Check for shortage/excess of refrigerant, poor condensation, choking in the refrigeration cycle, inefficient compressor, door leakage etc. and do the necessary repair or replacement
2. Adjustment of thermostat at very low temperature Note the thermostat setting and do the necessary adjustment or repair it or replace it.


Sr.No. Possible cause Check and remedy
1. Poor circulation of air inside  Insure refrigerator shelves are over crowded. If so, remove or adjust products to be cooled to permit better circulation of air.
2. Inside light is always on Observe door switch and its operation with the door. Repair it or replace it.
3. Excessive frosting on the cooling coil There is no freezing on evaporator coil. If it is there, switch off the machine to melt ice from the evaporator coil.
4. Leakage of air in the door  Door lining should be checked. Repair it or replace it to make sure that there is no leakage of cooling from the door.
5. Poor insulation of the cooling unit Fill the unit with proper insulation.



Sr.No. Possible cause Check and remedy
1. Dust on condenser There should be no dust on condenser, If it is there,wash it with water and clean with a soft cloth.
2. Frequent voltage fluctuations Are there  voltage fluctuations? Adjust it if possible otherwise close the unit for sometime till voltage is fluctuating.
3. Defective relay  If the relay is defective, then repair it if possible or replace it.
4. Choking in the system Improper cooling and cold condenser is the indication for choking. If the observation is yes, then replace the filter cum drier.
5. Overcharging of refrigerant Water on suction line is an indication of overcharging. If it is found, purge some refrigerant from the system.
6. Motor winding are week Check motor winding. If not proper, then get it rewound.


Sr.No. Possible cause Check and remedy
1. Light is always on Check door switch operation. If found defective, repair it or replace it.
2. Light is always on Check for the electric circuit of door switch. If found defective, repair it or replace it.



Sr.No. Possible cause Check and remedy
1. Improper leveling of the cooling unit Check the leveling of the unit. If found, adjust the base screws to level it.
2. Food stuff loosely placed inside .Check for food stuff. If found loosely placed, place it properly
3. Noise inside the condensing unit Compressor motor assembly not properly mounted on springs. Check if found noise inside, cut welding of the sealed unit and do the necessary repair or replacement.
4. Loose condenser coil Check for loose condenser coil. If found, do the necessary repair or replacement.




REFRIGERATION AND AIR CONDITIONING-TROUBLE SHOOTING-1        Refri Filling Blanks         Refri controls Filling blanks          Refri Trouble shooting-2           Refri Filling Blanks evaporators


Trouble shooting in refrigeration and air conditioning tells the faults of a system. Few precautions will make the system trouble free.



Sr. No. Cause Check and remedy
1. No electric power supply Test with test lamp for the availability of power. If not, write the complaint.
2. Discontinuity in circuit Check for continuity and do the necessary repair
3. Fuse blown Observe for fuse blown, if fuse is blown, then replace the broken fuse.
4. Overload protector burnt out  overload protector, if blown, replace the overload protector.
5. Too low voltage Measure for low voltage. If it is there, close the unit and write the complaint with the supply complaint office.
6. Thermostatic is in off position See for the thermostat for proper setting. If not, set it the right setting.
7. Relay defective Heck for relay. Start the unit without relay. If starts, replace the relay.
8. Stuck compressor Compressor may be  stuck. Start the unit without relay. If it does not start, then open the hermetically sealed unit and do the necessary repair.
9. Burnt motor There may be  no continuity in motor winding, if it is not there, get it rewound.


Sr. No. Cause Testing and remedy
1. No refrigerant in the cooling unit Run the unit. Touch condenser for hotness and evaporator for coldness. If results are found, check the unit for leakage first, repair for leakage if found. And only then charge the refrigerant into the unit.
2. Filter in Drier cum filter has choked Pinch off the tube at entrance and exit of the filter. Take out filter and replace it by a new filter.


Sr. No. Cause Check and remedy
1. Improper Thermostat setting Check for setting and do the necessary correct adjustment.
2. Shortage of refrigerant in the unit Run the unit. Check for frost on evaporator because of low pressure. Also check for condenser hotness. If it is less hot, then charge more refrigerant into the unit after insuring no leakage.
3. Excess of refrigerant in the unit See for sweating on suction pipe and condenser for excessively hotness. If it is there, then purge some refrigerant till the required conditions are achieved
4. Insufficient  condensation There is dust on condenser tubes. Check for fan speed. Proper cooling is not there. Clean the condenser tubes and do the necessary repair of the blower if necessary.
5. Compressor working inefficiently Observe for frosting on the evaporator tubes, cold condenser and warm suction line will tell about the inefficient working of the compressor. Open the unit and do the necessary repair of the compressor.
6. Tripping via overload protector Test the overload protector for its loose connections. Reduce cooling load on the machine or check by replacing the overload protector.
7. Wrong setting of thermostat Observe if the machine is stopping before reaching the required temperature or machine is not stopping at all. Check the thermostat and do the right setting of the thermostat.
8. The walls, roofs and bottom are poorly insulated Heat is constantly entering through the entire structure and it is appearing that the machine is not giving the desired cooling. Fill the required insulation where it is less.
9. Door not properly closed Check the lining in the door for its tightness. Check if the door is not tightly closed. Check for something which is not allowing the door to be tightly closed. Do the necessary repair or replacement to ensure tight closing of the door.
10. Inside light is always on Test the door switch. Check its operation by opening and closing the door time and again. If defective, do the necessary replacement.

FILL IN THE BLANKS-REFRIGERATION EVAPORATORS        Refri Filling Blanks         Refri controls Filling blanks          Refri Trouble shooting-2           Refri trouble shooting-1



Fill in the blanks will improve the deep understanding of a evaporator used in refrigeration. Evaporators are the cooling unit in a refrigeration unit. Both dry and flooded evaporators produce cooling using latent heat. Fill in the blanks for evaporators in refrigeration further increases practical knowledge.

  1. Evaporator used in the domestic units is called ————-evaporator.
  2. Commercial refrigeration uses an evaporator which is called ————-evaporator.
  3. Industrial refrigeration uses an evaporator which is called ————-evaporator.
  4. The evaporator is fitted between —————- and —————-.
  5.  Degree of super heat in dry evaporators is ————–.
  6. But flooded evaporator require   ————–degree of super heat.
  7. Standard degree of super heat  is ————–.
  8.  In actual practice, degree of super heat is ————–.
  9. Refrigerant evaporates in the evaporator by taking ——–heat in the evaporator.
  10. Evaporation of refrigerant is by taking heat from the ——–to be cooled in the evaporator.
  11.  Other name of evaporator is  ——unit.
  12. Pressure of the refrigerant is ——in the evaporator.
  13. Temperature of the refrigerant is ——in the evaporator.
  14. State of the refrigerant at the inlet of the evaporator is mostly————.
  15. At the outlet of the dry evaporator, state of the refrigerant  is ————-vapor.
  16. Name of the unit between the flooded evaporator and compressor is ————.
  17.  Expansion valve used with dry evaporators is ————-.
  18. The expansion valve used with flooded evaporators is ——-side float
  19. Evaporation temperature in the evaporator depends upon the ————in the evaporator.
  20.  Evaporator pressure is linked to the ——boiling point of the refrigerant.
  21.  Most of the evaporators have pressure  ———- atmospheric pressure.
  22.  Outlet of the flooded evaporator has refrigerant as  ——–and————.
  23. Material of the evaporator tubes is ————–with ammonia as refrigerant.
  24. Tubes of evaporator are made of  ————–with refrigerant R-134a.
  25.  COP of a refrigeration unit———–with the decrease of evaporation temperature.
  26. Power input increases as evaporator temperature ————.


  1. Dry, 2. Dry, 3. Flooded, 4. Expansion vale, compressor,,, 7.50C, 8. Variable, 9.latent, 10. Products, 11. Cooling, 12. Low, 13. Low, 14. Liquid, 15.saturated, 16. Accumulator, 17. Capillary tube, 18.Low, 19. Pressure, 20. Normal, 21. Above, 22. Liquid, vapor, 23. Steel, 24. Copper, 25. Decreases, 26. decreases