Drawbacks of running refrigerators - causes - remedies

Drawbacks of running refrigerators - causes - remedies

Drawbacks of running refrigerators

This guide designed and created by Itieffe represents a valuable resource for anyone involved in the design, maintenance or use of refrigeration systems and refrigerators. This guide has been developed to address a wide range of problems and inconveniences that can occur during the operation of refrigerators, offering a clear overview of the underlying causes and possible remedies. Before examining the specific content of the guide, it is important to provide a background to understand the context and importance of this resource.

Context of the use of refrigerators:

Refrigerators are essential devices in daily life and industry, used for the storage and refrigeration of food, pharmaceuticals, biological material and much more. Their reliability and efficiency are essential to ensure food safety and optimal preservation of temperature-sensitive products.

Inconveniences in the operation of refrigerators:

During their operational life, refrigerators can encounter a number of inconveniences that can negatively affect their performance. These issues can include refrigerant leaks, energy inefficiency, component failures, icing and more. It is critical to address these issues in a timely manner to ensure proper functioning and efficiency of refrigerators.

This guide is crucial for several reasons:

  1. Problem solving: provides a detailed guide to identify the causes of refrigerator problems and suggests appropriate remedies.
  2. Energy efficiency: helps improve the energy efficiency of refrigerators, reducing operating costs and environmental impact.
  3. Safety of food and temperature-sensitive materials: helps preserve the quality and safety of food and materials stored in refrigerators.
  4. Extended operating life: allows you to extend the operating life of refrigerators, avoiding irreversible damage and expensive replacements.
  5. Regulatory compliance: Helps ensure that refrigerators comply with relevant laws and regulations.

This guide is designed to be a practical and informative resource. Its content may include:

  • An overview of the main types of problems that can occur in refrigerators.
  • Detailed explanations of the underlying causes of each issue.
  • Tips and step-by-step instructions for diagnosing and solving problems.
  • Practical examples and case studies to illustrate the application of the proposed remedies.

In conclusion, this guide is an essential tool for ensuring the reliable operation and efficiency of refrigerators in a wide range of contexts. Its adoption helps to preserve the safety, quality and efficiency of refrigerated products and to reduce the maintenance and management costs of refrigeration systems.

Drawbacks of running refrigerators - causes - remedies

There are no machines that produce cold but there are machines that remove heat from everything around them. They are called: "Refrigeration machines"; they are made by closed circuits in which refrigerant gases circulate inside.

The refrigeration circuit (see Refrigeration circuit - The basics) is a complex machine that needs many components to work, which must be tuned together like an orchestra in order to function regularly.

When the refrigeration circuit fails, it is necessary to intervene with skill and practicality: this task is reserved for the refrigeration technician.

A good refrigeration technician must have knowledge of hydraulics, heat, electricity, mechanics, know how to weld and why not, chemistry. The refrigeration technician is a complete professional who embraces various sectors.

The main gift that a refrigeration technician must have is the perfect knowledge of the work that every single component and mechanical organ of the system must carry out.

Experience sharpens this skill and makes the refrigeration technician increasingly attentive to the situations he will find.

Having these bases, the technician will be able to diagnose any malfunction of the refrigerator and its parts and intervene for an immediate restoration of the same.

Recall on manometers and thermometers

The pressure gauges and thermometers are devices that help the refrigeration technician to analyze the closed circuit of the refrigerator. You have to know how to read and interpret them perfectly. For an overview, the tables of temperatures and pressures can be used (see: Refrigerant gas).

high pressure gauge

High pressure gauge

The high pressure gauge indicates the pressure of the gas and liquid (and the corresponding temperature of the saturated gas) and therefore the compression zone of the system from the gas outlet from the compressor head to the condenser and the tank upstream of the regulator. Any disturbance in this large area, such as poor air circulation to the condenser or poor water circulation to the water condenser, dirt inside the condenser, scaling, dirt on the condenser fins, internal greasing of the condenser pipes o of the liquid pipe, excess entrained oil, poor quality oil, excess liquid in circulation, clogging of the pipe, presence of air in the circuit, etc., give precise signals on the temperature and pressure (see Pressure conversions).

Therefore, how do you identify any or more of the aforementioned problems present in the system, if you do not know how to read the pressure gauge and the thermometer at high pressure, and if you do not know what the exact pressure and the exact high pressure temperature under normal operating conditions? For more details see the table Refrigerant temperature pressure ratio.

Bear in mind that when the system is stopped, the pressure indicated on the pressure gauge indicates the saturation pressure at the ambient air temperature or the temperature of the water circulating in the condenser.

Normal conditions

Under normal operating conditions the condenser is always hotter than the ambient air, and therefore the pressure inside this organ is always higher than that indicated by the tables or curves observed for a given ambient temperature.

 If the air condenser is correct, i.e. if its exchange surface is in perfect correspondence with the cooling capacity of the compressor, its internal temperature must be about 15 ° C higher than the ambient air and the pressure gauge will indicate a corresponding pressure. at room temperature increased by about 15 ° C. This means that the high pressure gauge reading does not give a precise indication but a very sufficient approximation, because we assume a difference of 15 ° C which is difficult to verify.

 In the case of the water condenser, the fluid inside the condenser must be at a temperature of about 5, or 7 ° C at most, higher than the average temperature of the water (i.e. the temperature of the inlet added to that of the outlet and divided for two.

Low pressure gauge

Low pressure gauge

The low pressure gauge indicates the evaporator pressure (and the corresponding saturated gas temperature) and therefore of the system in the suction part that goes from the area downstream of the regulating valve to the suction valve on the compressor. 

This pressure during the shutdown of the system will naturally be that corresponding to the internal temperature of the evaporator, as indicated in the tables (Refrigerant gas - fact sheets) or the pressure and temperature curves (and as indicated on the pressure gauge).

During operation, the pressure read on the suction pressure gauge will be lower than the real evaporation pressure.

The difference between these two pressures varies in each installation, because it depends on the pressure drop in the connecting pipes between the evaporator and the compressor, as well as on other factors, such as sections, slope curves, etc.

The thermometer

The thermometer is the tool that allows us to measure the temperature (see Temperature conversions).

The most used unit of temperature is the degree centigrade or degree Celsius proposed by the Swedish astronomer A. Celsius (1701 - 1744).

The degree is the hundredth part of the thermometric scale, obtained by setting the temperature of melting ice at 0 ° C and at 100 ° that of boiling water.

Besides the Celsius scale there are two other scales, the Réaumur used in France, and the Fahrenheit scale used in Anglo-Saxon countries.

The high and low pressure switch

High and low pressure switch

The double high and low pressure switch is a safety device that stops the compressor when the discharge pressure reaches abnormal values ​​above a fixed limit or when the suction pressure drops to abnormal values ​​below a certain value.

We remind you that it consists of two elements, membranes or bellows, sensitive to the delivery and suction pressures, which act on two electrical contacts from which the compressor motor is controlled (for high absorption it can control the coil of a remote control switch).

In contrast to the forces deriving from the pressures, they act on the control levers of the electrical contacts of the antagonist springs, the forces of which can be varied by means of adjusting screws.

By means of these adjustments, the maximum delivery pressure and the minimum suction pressure which must not be exceeded, i.e. the compressor motor stopping pressures, are fixed.

Indication of pressures

These pressures are indicated on two scales by movable indices connected to the adjustment screws (fig. 1).

The scale 1 on the left (in the type of pressure switch being analyzed) is that of the suction pressure (low pressure), while the scale 6 on the right is that of the pressure pressure (high pressure).

When the appliance is calibrated with the adjustment screws by setting a certain delivery pressure and a certain suction pressure, the pressure switch will cause the compressor to stop when the delivery and suction pressures reach the calibration values ​​indicated by the scale indices.

However, in order for the electrical contacts, once opened, to close again, the abnormal pressure that caused them to open must be brought back to the normal operating value.

If the shutdown was caused by too high delivery pressure, it will be necessary for it to drop to a lower and normal value; if the shutdown was caused by too low a suction pressure, it must go back to the operating value.

 The differences between the compressor stop pressures and the restart pressures are defined as the differential pressures or, more briefly, the differentials of the appliance.

1 - Low pressure scale.

2 - Low pressure adjustment screw.

3 - low pressure differential adjustment screw.

4 - Low pressure differential scale.

5 - High pressure adjustment screw.

6 - High pressure scale.

A - Low pressure connection.

B - High pressure connection.

Fig. 1 - High and low pressure switch (differential pressure switch).

The high and low pressure differentials can be fixed once and for all by the pressure switch manufacturer or can be adjusted with suitable screws.

 The type of pressure switch in fig. 1 has the high pressure differential fixed at the value of 3,7 bar (52,6 psi) indicated at the bottom of the high pressure scale 6 (in other types of pressure switches it may vary).

This means that whatever the intervention setting indicated on scale 6 for stopping the compressor, it will be restarted when the pressing pressure has dropped by 3,7 bar with respect to the stopping pressure.

In the pressure switch of fig. 1, the low pressure differential is instead adjustable, with a suitable screw, from 0,5 to 4 bar and the adjustment value is indicated by an index on the low pressure differential scale (4).

Differential pressure switches

The high pressure differential is kept fixed because the high pressure part of the pressure switch has only a safety function, and the fixed value of 3,7 bar allows the compressor to restart with a pressure difference compared to the stop sufficient to avoid oscillations or frequent stops and starts.

The low pressure differential, on the other hand, is adjustable since the low pressure part, as well as safety, can also have a regulating function. In fact, the low pressure switch frequently stops the compressor because it is no longer necessary to subtract the heat and put it back into operation when it is needed again.

Now let's see how to adjust the high and low pressure switch in fig. 1.

First of all, we note that the scales are graduated in pressure units both in the metric system and in the English system.

The pressures are relative and below atmospheric pressure the indication is in bar (metric system) or inches of mercury (in Hg - English system).

Stairs:

low pressure (1) ranges from 0,2 bar (5.9 in Hg) to 7,5 bar (108 psi).

of the low pressure differential (4) ranges from 0,5 to 4 bar (7,2 to 58 psi).

of high pressures (6) ranges from 6 bar (87 psi) to 32 bar (464 psi).


High pressure part adjustment.

You have an R404A system that works with a maximum condensation temperature of +35 ° C. A saturation pressure corresponds to this temperature (which can be obtained from the tables or diagrams - see Refrigerant gas cards) of 15,2 bar.

You want the compressor to stop when the discharge pressure reaches 17,3 bar corresponding to a temperature of about 40 ° C

From the diagram of the appliance it can be seen that the high pressure contact acts according to the diagram:

restart pressure = high pressure stop pressure - differential (calibration pressure scale 6);

and with numerical values: restart pressure = 17,3 - 3,7 = 13.6 bar.

 Therefore, by making the index of the relative scale coincide with the value 17,3 by means of the high pressure adjustment screw, the pressure switch will be adjusted for:

  • stop the compressor when the pressure reaches 17,3 bar;
  • restart the compressor when the pressure on the discharge side has decreased to 13.6 bar.

Low pressure adjustment.

 The low pressure contact operation diagram is as follows:

restart pressure = low pressure stop pressure + differential (calibration pressure scale 1 + scale 4).

The previous R404A system is always considered as it must operate with an evaporation temperature of -10 ° C to cool a cell to 0 ° C. A pressure of 10 bar corresponds to a temperature of -3.42 ° C.

 It is desired that the evaporation temperature does not drop below - 15 ° C, which corresponds to the pressure of 2,72 bar, at which the compressor must stop and furthermore it is required that the start-up is carried out when the suction pressure is rise to 4,41 bar, corresponding to a temperature of approximately -4 ° C.

 From the equality of the operating scheme we get:

differential pressure = restart pressure - stop pressure (scale 4 and scale 1);

and with numerical values: differential pressure = 4,41 - 2,72 = 1.69 bar.

The respective correspondence indices of 1 bar (4) and 4,41 bar (1) will be set with the low pressure (1,69) and low pressure differential (4) adjustment screws.

With these adjustments the compressor:

  • it will stop when the suction pressure has dropped to 2,72 bar;
  • it will restart when the suction pressure has risen to 4,41 bar.

ANALYSIS OF THE COMPONENTS OF THE SINGLE PLANT

Sometimes it is useful (even for those who want to create a database of the systems) to have the cataloging of the various system components.

Let's see what are the elements to be taken into consideration and related indications to be provided.

Compressor the number of cylinders, stroke and bore, number of revolutions making the ratio between the pulley diameters (see: Pulley diameters calculation) driven and driving and engine revolutions; the gas in use, whether hermetic or semi-hermetic, the power absorbed and the supply voltage (see: Characteristic values ​​of refrigeration compressors).

Electric motor (if compressor open) exact reading of the plate placed on the motor and therefore type of current, amperage, power factor, number of revolutions, voltage, power, diameter of the driving pulley, possibly measurement of the absorbed power (see Calculation of power and motor currents), diameter and type of the fan, type of terminal connections.

Condenser: if it is water or air, then. all the measurements relating to the shape, front development, and diameters of the pipes, number, size of the fins, path of the liquid, area cooled by the air and note how many rows there are, the way of attack of the gas at the inlet and outlet . If the condenser is water-based, measure the water temperature at the inlet and outlet, the flow rate, the exchange surface measured from the water side and from the refrigerant side.

 Liquid tank: its capacity (length and external diameter).

 Regulator: missing, type, characteristics, orifice (see detailed description of the defects at the end of the article).

Evaporator type

 Evaporator: type of evaporator, diameter, length of pipes, number of bends, quantity. of the fins and their dimensions, distance between the fins, surface, position of the evaporator, arrangement of the drip tray surfaces; whether dry or drowned or partially drowned.

 Fan: if it exists, give the characteristics of the current, the diameter of the fan, the number of blades, take the plate data if they exist, the power of the motor that controls it.

 Connecting pipes: diameter, length, arrangement

 Any devices: temperature exchangers, filters, dryers, other gear control devices. and safety: giving each of them the characteristics.

Running times of the compressor in 24 hours.

 Cell: internal dimensions (length, width, height); type of thermal insulation, thickness, arrangement, whether or not there is a layer for waterproofing, types of masonry; verification of the conditions of the environment outside the cell; weight of the goods introduced into the cell and rhythm of the incoming and outgoing goods; door opening rhythm; temperature of the goods when entering; storage temperature; number of doors and their width, their thickness and type of structure.


System malfunctions DURING WORK: CAUSES AND REMEDIES

We indicate some of the main and most recurrent defects that a plant presents during its work and of which we will try to explain them.

Defects can be caused by:

- thermal imbalance between the various parts of the system;

- imperfect positioning of the various parts of the system;

- imperfect thermal insulation;

- imperfect initial adjustment of the system;

- dirt in the system;

- humidity in the system;

- acidity of oils;

- bad quality of oils;

- failure in the mechanical part of the appliance;

- malfunction of the measuring and control devices;

- malfunction in electrical equipment.

Therefore what we will say is valid for the defects that most of all become evident. It should be noted that the causes listed below are the most common.

The following drawbacks can be observed.

1) The goods do not keep well, even though the right temperature is reached and the compressor works regularly.

2) The compressor always runs or runs for a long time without stopping and the temperatures reached in the cell are much lower than desired.

3) The compressor runs for a long time, that is, it stops only after a long period of working time, but nevertheless the temperature in the cell is not reached or after a long time and is kept for a short time.

4) The compressor does not turn at all and therefore does not remove heat from the environment.

5) The compressor runs without stopping and does not remove heat from the environment.

This chapter is put in the form of a table to give you a better view and understanding.


Synoptic table of major problems, causes and remedies in household and commercial refrigerators

Drawbacks

1st Case: The goods do not keep well, despite the fact that the right temperature is reached and the compressor works regularly.

 

POSSIBLE CAUSES

CHECKS, TIPS AND REMEDIES

From the fact that the temperature is reached in the cell and the compressor works with the right rhythm of attack and detachment, it is to be thought that the poor conservation of the goods depends on the poor circulation of the air in the calla and therefore it is good that the orientation of the searches is bandaged in that sense.

The goods smell bad and are damp; the flesh is soft.

a

Little volume of air circulates in the cell

Check the arrangement of the drip trays and if there is any frost piled up, or if the air circulation plates are regularly in place, as prescribed.

b

Too weak ventilation (in the case of a fan in the cold room)

Increase the fan power or observe if the evaporator is too closed by the frost; or if the position of the fan is faulty, correct it.

c

Insufficient and obstructed air passage

Clean, give a smaller temperature difference; move the thermostat to make a minor jump; remove any dirt.

d

Poor air circulation in the cell (circulation short circuits form, re-cycling the air exiting the evaporator).

Remove the obstructions that can determine the recovery of the air and also monitor the good distribution of the goods in the cold room

e

Bad arrangement of the goods in the cell. (gives rise to areas without circulation where the humidity and heat of the maturation of the goods accumulate).

Pay attention to the good distribution of the goods in the cell: correct.

f

Too much merchandise in the cell.

Pay attention to the good distribution of the goods in the cell: eliminate the extra goods.

g

The evaporator surface is too large in relation to the compressor power (and therefore the thermal difference between evaporation and calla is too small).

It is necessary to move the bulb towards the regulator or put a smaller evaporator; make sure that the temperature difference is between 8 and 10 ° C; much better than 6 ° C.

h

Presence in the cell of containers with liquid and not covered (the air of the cell in contact with the mass of the liquid absorbs humidity that deposits on the goods).

Put the lids on the uncovered containers.

i

Air entry from outside through doors, hatches, air vents.

Review all fasteners and fix or replace if they are not repairable.

l

The evaporator is too frosted (because the temperature difference is too strong and it is observed that the frost does not reach the thermostatic bulb).

Move the thermostat to have a normal temperature difference; or the evaporator has too narrow the intervals between the fins; and then replace it; or there is little fl uid in the system and therefore repeat an addition of fl uid; or the regulator is too narrow and needs to be opened; or the regulator is small compared to the cooling capacity and must be changed.

k

The compressor is too powerful and the running times are therefore very short (be careful, however, that during the winter, precisely due to the too low external temperature, even a normal summer compressor seems excessive during the winter).

It is better to put another compressor proportionate to the system.

If the meat loses weight because it is too dry and has the appearance of being covered with a parchment film, the causes of the excessive dryness of the meat are the following:

a

Too violent air circulation.

Reduce the power of the fan by replacing it with a less powerful one

b

Air thrown against the flesh.

Move the air jet against the ceiling and the return invests the meat

c

The thermal difference is too strong.

Move the thermostat and, if necessary, add another evaporating element

d

Compressor running time too long.

Move the thermostat for a correct adjustment, and therefore a lower gear.

e

Mechanical malfunction of the control devices.

If they cannot be adjusted, change them completely.

In almost all of the aforementioned cases, the compression gauge and the intake gauge will function indicating normal pressures. In case g) the evaporator pressure is too low, the compression pressure is normal. The same for case j).

2nd Case: The compressor always runs or runs for a long time without stopping and the temperatures reached in the cell are much lower than desired.

From the fact that the temperature reaches the exact one and falls even lower, it must be inferred that the major cause of the problem is to be found in the malfunctioning of the control devices.

 

POSSIBLE CAUSES

CHECKS, TIPS AND REMEDIES

a

Control devices disconnected or not regulated.

Check, modify and replace if necessary.

b

Short circuit in the electrical lines of the control equipment.

Check and overhaul, and if necessary replace and arrange in the workshop.

c

Control devices blocked.

There may be dirt or water and then repair under normal conditions.

D

Regulator closed badly that the ax escape the liquid fluid.

It is repaired in the way already said at the time for the simple automatic regulator or for the thermostatic one.

e

Thermostat or thermostat bulb loosely or loose.

Check and tidy up.

f

Overheating does not work well because the bulb is detached.

Put the bulb back in order and check the length of the dryer tube after the bulb.

In these cases normally the suction pressures are very low, more than normal, and the pressure of the pressure are high, because the gas arrives very hot (except in case f).

3rd Case: The compressor runs for a long time, that is, it stops only after a long period of working time, but nevertheless the temperature in the cell is not reached or after a long time and is kept for a short time.

 

POSSIBLE CAUSES

CHECKS, TIPS AND REMEDIES

That is, we have long periods of work and very short stops. The cold is reached after a long time and is kept for a very short time. We call this compressor running mode "short cycle".

The causes are of different nature and we will try to give the main ones. Generally, however, the drawbacks are due to the mechanical parts of the system which function badly.

a

Very dirty air condenser.

Clean the condenser.

b

The air condenser receives little fresh air because the room is insufficient.

There is no other remedy than to increase the mass of air that goes to the condenser and that it is fresh.

c

The condenser fan gives little air.

Change the direction of the blades; or move the condenser away from the wall; or put another fan with larger diameter or wider blades.

d

If the condenser is water-based it is scarce or dirty or is already hot.

All you have to do is increase the quantity of water so that the temperature difference between the inlet and the outlet is about 8 ° C; if dirty, clean it by passing it through a filter; or take water from another source; if it is hot and you can't have another one, try to cool it with an evaporative tower.

e

Presence of air in the circuit.

Eliminate it in the known ways.

Keep in mind that in all these cases the pressure pressure is always much higher than normal and the energy consumption is exaggerated; the suction pressure is higher than normal; the compressor works hot, the condenser is very hot.

If you have a pressure switch, it comes into operation at very short intervals, because the maximum pressures from its detachment are quickly reached.

Other inconveniences outside the compressed area.

a

The dehydrator is blocked.

Clean it and replace the desiccant mass

b

The filter is blocked.

Clean it.

c

The thermostatic valve or automatic regulator is no longer regulated.

Adjust it, and if not possible, replace it completely.

d

The simple regulator or thermostat gives a little stroll to the liquid.

Clean and adjust it; if, on the other hand, it is small compared to the power of the system, replace it.

e

Lack of liquid.

Add fluid.

f

The compressor quickly goes into vacuum and the low pressure switch often cuts off the current.

It is certainly necessary to increase it at the minimum opening of the regulator. Repair and if necessary, if the fault is in the regulator, replace it.

g

The low pressure switch (draft gauge) is faulty.

Exchange it with another coupon.

h

The high pressure switch is faulty.

Exchange it with another coupon.

The pressures have variations in the circuit and precisely the suction pressure falls in cases a), b), d), e), f).

The pressing pressure drops in cases a), b). c), d). And).

In almost all cases the signals made by the pressure gauges are imperfect.

4th case: the compressor does not turn at all and therefore does not subtract heat from the environment or subtract little of it

The causes are to be found in two orders of factors; that is, in the refrigeration field and in the electric field; let's see them separately.

Causes of refrigerator order

a

The thermostat is out of control, or it is blocked, or it is always open.

Check the thermostat in the known ways. If necessary, put a new one.

b

Unregulated or defective pressure switch.

Check as described above and eventually replace it with another good one, and then check in the workshop.

c

Good pressure switch, check:

1) if the regulator is blocked, closed;

1) Check and repair or replace the regulator.

2) if the bulb is empty;

2) Check and repair or replace the regulator

3) if there is paraffin in the regulator;

3) Clean the regulator and change the oil.

4) regulator filter blocked;

4) Clean.

5) system filter blocked by dirt;

5) Clean and replace if necessary.

6) clogged dehydrator;

6) Clean and, better still, remove the old desiccant and put in the new one.

7) liquid line blocked;

7) Clean and tidy up the desiccant and filter.

8) scarcity of fluid;

8) Refill or add.

9) if the compressor is subjected to external cold in winter, the pressure does not reach the motor.

9) Protect the appliance as previously said and, better still, put the appliance inside a room.

In all the aforementioned cases the compression pressure will remain very low: the compressor will be partially cold, the suction pressure will also be low or normal.

Causes of electrical order

a

The engine does not run.

Check if the current reaches the motor terminals.

b

Blown fuses.

Check and repair by replacing them; check the cause of the fusion.

c

Power wires cut.

Repair.

d

False line contacts.

Repair.

e

Disconnected circuit breaker.

Repair.

f

Coil broken.

Replace the motor.

g

Check all possible faults, as reported at the time, for the motors and repair accordingly.

 

5th Case: The compressor runs without stopping and does not subtract heat from the environment or subtract little of it

There may be a shortage of power supply to the evaporator, therefore producing little cold; little frost; low compression pressure; low compression temperature, low inlet pressure; low temperature on intake. Causes:

a

Motor compressor unit too small.

Replace it with another one of increased power

b

Partially blocked dehydrator.

b) Clean it and replace the desiccant.

c

Partially blocked filter.

c) Clean it.

d

The liquid line is partially blocked.

d) Clean and put a more effective filter

e

Moisture in the circuit.

e) Remove the humidity with known methods.

f

Partial obstruction due to the paraffin of the oils.

ƒ) Clean and replace the oil.

g

Small opening of the regulator.

g) Open more.

h

Poor capacity regulator.

h) Replace it with another suitable one.

i

i) Bulb partially discharged.

i) Replace the entire thermostatic valve.

If, on the other hand, the supply of fluid in the circuit is sufficient, the reasons for the malfunction must be found in the excessive mass of fluid; and therefore:

a

very open regulator.

A) Close the regulator a little or replace it with a smaller one if the capacity is too large.

In this case the condenser pressure is too high but the compressor is frosted, the suction pipe is too frosted. The condenser is cold.

 

If there are gas leaks due to poor sealing of the compressor valves, the discharge pressure and temperature are lowered.

Disassemble the compressor, check for damage and replace faulty parts or repair them.

If the compression temperature is too high, the condensation pressure is also high and the problem is due to:

a

The condenser is dirty or the air is insufficient or the air is too hot.

a) Repair in the ways already mentioned before.

b

The condenser has water that is too hot or dirty or insufficient.

b) Repair as already said about it.

c

The flywheel is slightly unlocked.

c) Check and repair.

d

The evaporator is excessively frosted.

d) Repair as already mentioned at the time.

Other operating problems

We have examined the various consequences of a faulty installation or an imperfection in some refrigerating organ; now we think that it is useful for the refrigeration technician to see how some imperfections in the system can cause problems. Of course, defects are often due to the same causes, but precisely since the circuit is closed, it is good to see if some of the system or operating defects affect other parts of the same installation.

The most frequent causes can be specified below:

1) Insufficiency of refrigerant.

2) Obstruction in a pipe.

3) Gas leakage through the compressor valves (i.e. insufficient seal of the valves).

Let's see what problems they can cause in the system.

You have a cell or a cabinet with a thermostatic valve and a pressure switch.

Cause: Insufficient refrigerant.

Drawbacks:

a) little refrigeration;

b) suction pressure too low;

c) the group has short stops (ie runs often);

cl) the regulating valve blows;

e) the suction line is hot;

ƒ) the evaporator is not completely frosted.

The blowing regulating valve is the precise indication that the refrigerant is low in the system, and opening the valve does not increase the refrigerant effect. On the contrary, it can be seen that the little passing fluid evaporates immediately, producing frost near the valve, without spreading out in the evaporator, and remains very distant from the thermostatic bulb. Of course there is not enough cold; the gas reaches the compressor too dry and therefore the suction line is hot and the thermometer indicates this condition, while the pressure is low; and as you work the pressure is lowered more and more. For the room thermostat to reach the right detachment temperature, the group must work for a long time. As soon as the set temperature has been reached, the thermostat switches off the power and the compressor stops; but the heat that enters from the outside causes the temperature in the cell to increase rapidly and therefore the thermostat raises its temperature, reconnects the electrical line and starts the compressor again. There will therefore be a long period of work and a very short stop.

Remedy: eliminate the leak and increase the quantity of liquid in the circuit by recharging

Obstruction in a pipe.

Drawbacks:

a) the group continues to work without stopping;

b) there is no frosting;

c) the suction line is hot;

d) the evaporator is hot;

e) the temperature in the cell or in the cabinet is not reached;

ƒ) the suction pressure drops more and more until it works in vacuum.

When the pressure drops and tends to vacuum, it is immediately necessary to think that there is an obstruction in the suction pipe. By checking the pipe, you can see the point of obstruction, because upstream of it the pipe is black and downstream it whitens and a ring of frost forms.

Of course the evaporator cannot cool down; the suction tube is not cold either; the suction pressure gauge tends to go to vacuum; the compressor is hot and as the desired temperature is not reached, the engine never stops.

We can find the obstruction either in the pipe or in the valve; or at the liquid start tap.

If the obstruction is in the pipe, as we have said, we observe a ring of frost in the point where there is the obstruction; if it is in the liquid starting tap then it is advisable for this tap to be opened and closed more than once and quickly. Often this way the dirt escapes, but it certainly goes into the regulator valve which will become clogged. It is therefore necessary to eliminate the problem by inserting a filter or to clean the existing one which will most likely be dirty.

If the obstruction has occurred in the valve, and therefore in its seat, act on it by suddenly opening and closing the passage and when it is observed that the dirt has passed, try to eliminate it with a new filtering of the system.

The obstruction can normally be caused by the presence of dirt, or by copper burrs, or by paraffin or oil gums, or by powdered calcium chloride, or by another cause.

If when cleaning the filters we notice the poor quality of the oils or fluids, the best thing is to completely change the oils and fluids.

Remedy: indicated directly in the previous content what are the operations to be done in this regard.

Cause: Insufficient sealing of the valves.

Drawbacks:

1) If the escape is weak:

a) the suction pressure is a little lower than normal;

b) the group runs for a long time;

c) the refrigeration is not intense;

d) the pressing pressure is low;

e) the evaporator is lightly frosted or wet (sweaty).

The pressure or suction valves can be deformed or hold badly in their seats, or have dirty seats or their springs do not work as they should.

Remedy: replace them if they cannot be repaired.

2) If the escape is strong:

a) the suction pressure is very low;

b) the group never stops;

c) the refrigeration is too weak;

d) the pressing pressure is very low;

e) the evaporator is lightly frosted or wet (sweaty).

The phenomena recorded here are the same as the previous ones except that they are more intense, because the inconvenience is greater.

Remedy: Replace defective parts or repair them on site if possible.

Please note: if the operation of the system is normal and the goods enter the cold room at the expected temperature, the long operation of the system can be thought of due to the compressor valves, which do not have a good seal. To check this, close the suction tap on the compressor and observe the suction pressure gauge. If it does not go towards the void, three causes can be thought of:

1) the intake valve does not hold;

2) the pressure valve does not hold;

3) the suction valve and the pressure valve do not hold both.

Let's see the three cases one by one.

1) The suction valve that does not hold is checked in this way: the pressure cock on the compressor is closed and the pressure gauge decreases and the suction pressure increases; this is because the gas passes from the top to the bottom; therefore in the equilibrium the upper part is lowered, the lower one rises, up to an average pressure; that is, the gas from the top passes into the crankcase increasing the suction pressure.

2) The pressure valve does not hold: it can be checked by closing the suction cock. If the compressor fails to vacuum, it means that, as the suction cock is closed, gas enters from the broken or blocked pressure valve.

3) The suction valve and the pressure valve do not hold both: the check is carried out by carrying out the operations referred to in points 1 and 2 successively.

Naturally, all these causes lead to the consequence that the normal pressing pressure is never reached, the suction pressure is not even reached completely, and in operation the operating pressure and temperature are never reached to allow the thermostats to work. to the high or low pressure switches;

It is sometimes necessary to think that the desired temperature is not reached well in the cell, because this has not been constructed and insulated in the right way and therefore there are many dispersions. In this case the walls, ceiling and floor are wet with water drops or covered with ice.

Other drawbacks: causes and remedies

We believe it is opportune to report other observations on how in general the possibilities of controlling the plant can be presented

 The compressor runs with short cycles (ie the compressor: when it starts, it makes short strokes and the stops are also of short duration).

Probable causes:

  • The control temperature of the appliances is too high.
  • If the control is with a pressure switch it means that the regulator never closes.
  • The differential of the thermostat or pressure switch of the group is too small.
  • The delivery valves do not rest well on their seats and the pressure switch does not intervene.
  • The compressor is more powerful than necessary.
  • The compressor runs at high speed.
  • The high pressure switch does not work properly.
  • The pressure at the pressure switch is not reached due to insufficient fluid (the pressure at the pressure gauge is very low and the pressure temperature is also low).
  • The thermostat bulb on the evaporator is placed very close to the regulator.

The compressor runs with too long cycles (i.e. the compressor works for a long time before stopping).

Probable causes

  • Lack of charge (it should also be noted on the suction manometer a low pressure and the temperature instead is high).
  • The compressor is too weak for the system.
  • The compressor runs too slowly.
  • The differential of the thermostat or pressure switch is too large.
  • The room thermostat is badly set up.
  • The contact thermostat bulb is badly connected on the evaporator.
  • Bad condensation or due to insufficient air or too hot air (in the case of an air condenser) or insufficient or dirty water or hot from the beginning (in the case of a water condenser). High malt pressing pressures are observed.
  • Evaporator too small.
  • Evaporator too frosted.
  • Poor air circulation in the cell, which does not affect the bulb of the room thermostat well.
  • Poor thermal insulation of the cabinet or cold room.
  • Air entry through the doors due to poor sealing of the fixtures.
  • Too frequent opening of the doors and therefore poor management of the system.
  • Arrival of too hot food.
  • Poor regulation of the simple or thermostatic regulator.
  • The shutter of the regulator does not rest well on its seat.
  • The compressor has mechanical defects.

The evaporator is too hot and takes away little heat.

Probable causes:

  • The pressure switch or thermostat is set for too high a pressure or temperature.
  • Air entry through the door.
  • Poor or defective thermal insulation.
  • The evaporator is too frosted.
  • The evaporator has a badly adjusted regulator.
  • Lack or insufficiency of fluid; the regulator is heard whistling, and it is also observed that the suction pressure is very low.
  • Slightly clogged filter.
  • Poor air circulation on the evaporator.
  • Poor air circulation inside the cell.
  • The compressor is of insufficient power.
  • The evaporator is too small.
  • The compressor has mechanical defects.
  • Bad arrangement of the goods.

The evaporator has too low a temperature.

Probable causes

  • The pressure switch or thermostat is set too low.
  • The thermostatic bulb is badly fixed to the evaporator.
  • The pressure switch is short-circuited.
  • The thermostat is short-circuited.

The compressor runs continuously.

Probable causes

  • The pressure switch is short-circuited.
  • The thermostat is short-circuited.
  • The thermostat bulb is exhausted.
  • The thermostat bulb is badly fixed to the evaporator.
  • Lack or insufficiency of refrigerant fluid, which can be observed by checking the pressing pressure which is very low and the suction pressure is also low; the pressing temperature is low, while the suction temperature is high.
  • The refrigerant does not reach the regulator due to an obstruction on the liquid line.
  • The regulator is blocked by the formation of ice due to humidity in the circuit.
  • The regulator is blocked due to dirt in the open position.
  • The condenser works badly due to hot air, or because it is dirty, or due to insufficient air.
  • The condenser is malfunctioning because the water is hot, insufficient, or encrusted.
  • The compressor is of insufficient power.
  • The compressor is in poor mechanical condition.
  • The evaporator is too small for the required power.
  • The evaporator is too frosted.
  • Insulation is insufficient.
  • Air enters through the doors.
  • Operation of the plant is incorrect.
  • The incoming goods are excessively hot and badly stacked.

The pressing pressure is too high.

Probable causes:

  • The regulator is too open.
  • There is air in the circuit.
  • The compressor is placed in a room that is too hot or too small.
  • The capacitor is too small or badly arranged.
  • There is insufficient air circulating through the condenser.
  • The air condenser is dirty.
  • The water condenser has insufficient or dirty or hot water.
  • The water condenser has encrustations.
  • The fluid charge is excessive and therefore the pressure is high and the temperature is low.
  • The water valve is throttled or dirty (case of water condenser).

The pressing pressure is lower than normal.

Probable causes:

  • Lack or insufficiency of refrigerant.
  • The compressor has valves and piston rings that are not holding.
  • The power supply to the evaporator is insufficient due to lack of opening of the regulator or presence of dirt or humidity.
  • The liquid line is blocked.
  • The regulator is too closed.

The suction pressure is too high.

Probable causes:

  • The valves are defective and the compressor does not suck.
  • The regulator is too open.
  • The thermostatic bulb is faulty or exhausted.
  • The thermostatic valve has failed its seat.
  • If the evaporator is supplied with a float valve, the seat or shutter of the latter may be faulty or blocked.

The suction pressure is below normal (the case is similar to the previous one but with less intensity).

Probable causes:

  • The regulator is clogged with ice or dirt or is improperly adjusted.
  • The filter is clogged.
  • The dehydrator is exhausted and no longer retains moisture.
  • The liquid start valve on the tank is not open enough.
  • The refrigerant is insufficient (the regulator can be heard whistling).
  • The section of the liquid line is too small and therefore the pressure drops are excessive.
  • The suction pipe is broken in some places.

Abnormal noises during operation.

Probable causes:

  • Shock absorbers that are too dry or broken.
  • Suspension (if any) broken or faulty.
  • Poorly fastened pipes due to loss of clamps or broken clamps.
  • Badly tightened bolts.
  • Lack of oil in the crankcase.
  • Game in the pin.
  • I play in the eccentrics or in the connecting rods.
  • Broken valves.
  • Blowing of gas leakage sealing devices.
  • Splashes of liquid or oil hits in the compressor head.
  • Bad fastening of the flywheel.
  • Slow straps.
  • Fan propeller touching the condenser.
  • Lack of alignment between engine pulley and flywheel.
  • Water valve that vibrates due to bad regulation.
  • Pressure valve that vibrates due to insufficient oil inside.
  • Solenoid valve vibrating due to bad placement or incorrect voltage.
  • Check valve that vibrates (especially if it is placed vertically and then it is good to put it at 35 ° or 45 °).

Evaporator making noise.

Probable causes

  • Badly secured evaporator.
  • Piping that reaches the evaporator badly fastened and resting on the evaporator.
  • Badly fastened drip tray supports.
  • Air duct supports (if any) badly secured.

Odors in the cell or closet or outside such compartments.

Probable causes:

  • Bad air circulation.
  • Escape of the refrigerating fluid.
  • Odor due to bad insulation or bad waterproofing or painting of the walls.
  • Burning of the electrical insulation.
  • Heating of paints or synthetic rubbers.

Bad smells in the calla must be eliminated further with normal cleaning, by placing goods in the cell that are not already initially damaged; use the ozonator and provide for appropriate air renewals.

Noises in the system

The noises heard in a running system refer to the noises perceived in the compressor and in the condenser or evaporator.

For those on the compressor, the causes may be different, including those of pure mechanical and external origin, such as: - the crankcase bolts which are not properly tightened, - the flywheel not properly fixed or the key on the flywheel is broken, - the drive belts are slow and not adherent to their seat slip from time to time, - the propeller. of the fan sometimes crawls on the fins of the air condenser, - due to lack of alignment between the pulley and the flywheel, - the water valve that vibrates because its regulation is not correct for the pressure with which the water arrives, - compressor arrival and departure pipes not well fixed to their clamps, - shock absorbers not tightened.

The noises inside the compressor and for mechanical reasons can be caused by: - ​​lack of oil in the crankcase, - excessive play in the piston pin, - excessive play in the eccentrics and connecting rods, - valves or springs of these routes, - blow to the sealing device for gas leakage, - liquid blows on the compressor head due to too open regulator or gas condensed in the suction pipe after a long stop in a cold environment, - oil blows due to long running of the compressor under vacuum, - pressure valve which vibrates due to insufficient oil in its interior.

Among the noises caused by the evaporator we can mention the most normal such as: - loosening of the tightening of the bolts that fix the evaporator to the ceiling or walls, - the piping that arrives or starts vibrating because it is badly fixed to its brackets or underneath the flow of air moved by the fan, - the drip supports not well tightened, - the supports of the air ducts that have loosened, - excessive speed of the air in the delivery ducts if they are made especially of sheet metal.

Once identified, all the aforementioned noises, to the compressor, the condenser and the evaporator, can be easily eliminated, and therefore it is advisable to proceed with their total elimination, without allowing time to pass, because their persistence, very often then generates serious inconveniences, for which it is necessary to intervene at higher costs.


Adjustment of thermostatic valves: problems, causes and remedies.

In particular, let's analyze one of the essential components of the refrigeration circuit: the thermostatic valve.

Most of the problems in the operation of the thermostatic valve depend on the bad position of the bulb or on its not perfect adherence with the evaporator tube.

The final adjustments of the thermostats must guarantee that they are correct and durable, they must be carried out for the final touch-up, when the whole system and the cell are already in perfect working order.

When in a system it is necessary to disassemble the thermostatic valve for a repair or replacement, it is necessary to make sure that it has a pressure inside it equal to the atmospheric pressure or just higher in order not to let air and therefore humidity enter, and then that can be put back in order without breaking down the vital parts of the appliance.

To disassemble a thermostatic valve on site, you start by making a vacuum in order to transfer all the liquid into the tank;

  • then a small quantity of fluid is introduced into the liquid pipe, so as to have a pressure equal to zero or slightly higher, so as not to let air into the regulator;
  • finally, the regulator is disassembled, taking care not to “contaminate with humidity” the inside of the gas pipes.

If, on the other hand, in the final adjustment operations you have to turn the appropriate screw at the head of the valve, unscrew the cover, give the screw one turn or part of a turn and immediately close the cap again. The opening and closing direction of the screw to regulate the gas flow is different according to the type of valve used.

The adjustment must be carried out after at least 24 hours that the appliance and the cell are in perfect working order.

Good regulation is indicated by the mass of frost on the evaporator: if the frost reaches the end of the evaporator, the regulator has reached its correct opening; if the frost passes the end of the evaporator, the regulator is too open; if the frost does not reach the end of the evaporator, it means that the regulator is too closed.

If the compressor is proportionate to the evaporator, we will have regular frosting, and therefore the pressure inside the evaporator is in direct function with the evaporation temperature and this with the temperature to be reached in the cell. This indicates that the evaporator is perfectly used. Therefore there is perfect balance between evaporator and compressor.

But if the evaporator is smaller than the desired one, then the compressor is more powerful and the equilibrium in the evaporator will be obtained with a lower pressure than necessary, in order to have the desired temperature in the cell. In other words, the thermal difference between evaporation and the temperature of the calla is too strong: the frost is dry and abundant, too adherent to the evaporator and hard to come off.

But if the evaporator is more abundant than necessary, or the compressor is weaker, the equilibrium will be produced at a higher pressure, i.e. the temperature difference between the gas inside and the temperature of the calla is small, the frost Sara. light, wet and easily detaches as soon as the implant is stopped.


Defects that can occur while driving.

The thermostatic valve is not well adjusted or is completely blocked.

Let's see the two flaws:

a) Bad regulation:

The following cases can occur:

1) The cell is cold at normal temperature but the compressor works for a long time

  • The cause of this problem: it is a poor supply of the evaporator caused by bad regulation of the valve.
  • Insufficient power supply causes a lowering of the evaporation pressure and therefore a lower yield of the compressor with consequent long periods of operation.

2) The cell has the desired temperature and the compressor works without stopping

  • The cause of this inconvenience is that the thermostatic valve is closed much more than necessary, this represents the extreme case of the previous defect.
  • In both cases, as well as the abnormal operation of the compressor, it is noted that the suction pipe is colder than necessary.

To make sure that the adjustment is not correct, the recommended operations are as follows:

  • vacuum the system, stop the compressor, then completely close the regulator and finally quickly open the liquid cock on the tank. In this way; upstream of the regulator, we have the liquid pressure. If the shutter of the regulator lets liquid through because it is not closed correctly, the pressure in the evaporator will rise rapidly; if the shutter is closed properly, the pressure inside the evaporator will rise very slowly.
  • It has been found that the shutter closes badly, to improve regulation, vacuum again and then quickly open the liquid tap. Repeat the operation until you have accommodated the correct opening of the regulator.

b) The thermostatic valve is blocked.

The following cases are observed:

1) There is no cold in the cell and the compressor naturally continues to run

  • Cause: if the gas does not pass, there is no cold in the cell because there is no evaporation, and therefore the thermal difference between evaporation and cell is zero. The compressor in turn continues to work because the temperature in the evaporator has not been reached.
  • the cause of the problem may be due to humidity in the system which has produced a drop of ice in the seat, or to dirt in the system which has blocked the valve, or acidity of the oil or bad oil which forms paraffins.

c) The pressure inside the evaporator is too low

  • Cause: the gas passes but in a minimal quantity, precisely due to the obstruction of the valve. The little gas expands at an increasingly lower pressure and therefore there is a small thickness of crystalline frost in the tube. Let's go back to the previous cases.

Remedies:

If the cause is due to humidity, just wet the head of the regulator with a rag soaked in hot water, the ice melts and the obstruction ceases. However, since the problem will easily recur, it is necessary to put a good dehydrator in the circuit. If the dehydrator is present it means that it is exhausted and it is necessary to replace the dehydrating mass or the filter itself.

If the cause is dirt, it is good to put a good filter or clean the existing one and in the meantime give a few sharp blows of liquid, acting on the tank tap, as said for the previous analogous case.

If the cause depends on the oil, change it completely.

If the cause is rupture of the thermostatic valve, replace it.

Insights

Thermostatic valves are very sensitive to irregularities that the system presents (which almost always cause serious problems) such as:

- dirt in the system;

- humidity in the system;

- acidity of oils;

- paraffins in oils due to their bad quality;

- wrong capacity of the valve with respect to the power of the system.

As regards the cause of the problems that thermostatic regulators can present, the following cases can be observed:

a) The thermostat is of insufficient capacity.

This means that not enough liquid passes through its fully open valve seat, which evaporating gives the right amount of heat subtraction to the cell to lower its temperature. The gas pressure can become much lower than normal, the frost is too close to the thermostat and away from the bulb. Put your hand on the thermostat bulb, in order to observe if by chance the valve opens more. If it opens, then gas enters the evaporator and you will see that the frost returns to the bulb. If all this does not come true, it is necessary to completely change the thermostat and put one with a higher capacity.

b) The thermostatic valve is stuck closed.

The same problems will occur, caused by humidity, dirt, acidity of the oil, presence of paraffin, mechanical defect of the valve itself.

c) The sensitive element is discharged.

For any accident (blows, bumps, rust caused by external humidity, etc.) a small hole may have been produced in the bulb or in the capillary tube or in the bellows or on the membrane, then there will be an imperfect refrigeration, an imperfect frost, a long period of operation of the compressor and sometimes the compressor works without stopping.

Try putting your hand on the bulb of the thermostatic valve; if the problem is not very serious, the frost will spread. on the evaporator tube and if this is not achieved, then it is recommended to replace the valve with a new one.

d) The thermostatic valve is stuck open.

Excessive power to the evaporator occurs; the frosting of the suction pipe goes beyond the bulb of the thermostat and can reach the compressor with the possibility of dangerous liquid returns. Try to vary the valve setting by trying to slit it; if no result is achieved, replace the valve.

e) The thermostatic valve has been incorrectly adjusted.

If it is too open we will have that the suction pipe after the thermostatic bulb is frosted or sweats. Then it is necessary to tighten the opening of the valve a little, that is to bring the shutter closer to its seat with a fraction of a turn. If you still don't get any money, then try to get the shutter all the way down. If, despite this, the frost always remains beyond the thermostatic bulb, it means that the valve is too large for the system and it is therefore advisable to change it with another one more proportionate to the installation. If the valve is too closed we will have the cases already seen in paragraph b.

Always remember that the adjustment is done in fractions of a turn at a time, the cap must be put back in place immediately after each adjustment. If you have to replace the valve, bear in mind the possibility. of air entry into the system and therefore see what has been said about it.

f) The filter of the thermostatic valve is blocked by dirt.

 Disassemble and clean it. But put a clean and effective filter in the circuit and avoid the repetition of the problem. The filter on the thermostatic valve must provide for the retention of impurities only in the event that a minimum quantity of dirt escapes from the system filter and must never replace it in function.


A study is provided below for the drawbacks that the presence of the thermostatic valve can cause in a refrigeration installation.

 

Overview of the problems caused by the thermostatic valve

Drawbacks

Causes Remedies

a

the regulator blows

Lack of fluid; partial obstruction on the liquid line; the liquid line is too long; the condenser is too cold (because it is placed in a colder compartment than the cell).

Remedies: refill with gas; clean the pipes and check the effectiveness of the filter, replacing it if necessary; try to shorten the distances between the unit and the evaporator or put a larger tube for the liquid; move the condenser or group to a warmer compartment or protect the group against cold.

b

the system empties

The bellows of the thermostat is broken.

Remedy: replace it.

c

the regulator locks up after a long period of operation

Moisture present in the circuit that forms an ice plug.

Solutions: unblock the valve by heating it and replace the dehydrating mass: of the filter.

d

thermostat too small

With the valve fully open, the liquid that passes is not sufficient to give the desired temperature in the cell; stopping the group the thermostat does not close.

Remedy: change the thermostat with another more suitable one.

e

non-watertight thermostatic packing gland or defective seals

Gas leak; the system empties

Remedies: change thermostat

f

Badly adjusted thermostat

The room temperature is not reached

Remedy: open the valve until complete adjustment

g

Obstruction in the thermostat seat

The cell is hot; the suction pressure is too low; the compressor does not stop; the thermostat filter is perforated

Solutions: change the thermostat filter

h

Oil in the thermostat chamber

Little yield of the plant

Remedies: heat the valve with a cloth soaked in hot water; stop and quickly open the valve

i

The capillary tube of the thermostat is broken

The valve is always closed and the suction pressure tends to vacuum

Remedies: change thermostat

j

The thermostatic train bulb is empty

The valve is always closed and the suction pressure tends to vacuum

Remedies: change thermostat

k

Clogged circuit filter

The plant tends to empty; the suction pressure is lowered more and more

Solutions: clean or replace the filter

l

Ice in the thermostatic valve

Presence of humidity in the circuit

Solutions: replace the filter drier

m

Blocked valve

The system tends to vacuum and the suction pressure is always lower than normal

Remedies: change thermostat

n

The thermostat is in a colder environment than its bulb

The thermostat remains closed because the bulb, while heating up, will not be able to push the shutter

Remedies: Change position of the thermostat


The use of the capillary tube and relative warnings

The capillary is a function (in terms of diameter and length) of the evaporation temperature.

It must be premised that the condenser must not have a liquid reservoir, because this must not remain in the condenser but pass everything through the evaporator. The presence of the tank would cause the liquid pressure to drop. The liquid would accumulate in very small quantities in the lower part of the condenser, forming a plug at the inlet of the capillary tube.

A small filter is provided at the output of the capacitor.

The fi g. 2 gives an idea of ​​the distribution of the fluid in the circuit in regular running. The capillary tube which acts as a heat exchanger is welded to the cold gas pipe for at least 1,50 m. In normal operation the condenser is very hot in the upper part, for a short length (due to the overheating of the compression), followed by the rest of the condenser with uniform heating. The evaporator is uniformly cold and the temperature is reached in the compartment to be cooled.

Fig 2

Fig. 2 Generic circuit with capillary with regular operation.

1 - compressor

2 - capacitor

3 - filter

4 - capillary

5 - heat exchange area

6 - evaporator with liquid (regular)

If the evaporator is completely frosted the condenser is too hot for several turns and the lower ones are warm.

This is the proof. that the capillary offers a lot of resistance to the passage of the liquid.

Little passes, everything evaporates, fills the evaporator with frost and the gas overheats upon compression.

The liquid not passing through the evaporator accumulates in the last turns of the condenser (see fi g. 3).

Fig 3

Fig. 3 Generic circuit with capillary but faulty.

1 - compressor

2 - condenser with liquid (irregular)

3 - filter

4 - capillary

5 - heat exchange area

6 - evaporator with reduced evaporation

To overcome this drawback it is necessary to shorten the capillary tube to give less resistance to the liquid.

If the evaporator is hot, the condenser temperature high at the top and decreasing at the bottom, and the cell is cold, it means that there is air in the system that needs to be eliminated.

If the evaporator has little frost, the upper part of the condenser is not very hot and its lower coils are cool and the cell is hard to get cold, it means that there is little gas in the circuit or the pipe is too short. You make a gas charge and if nothing is resolved you have to put on a longer tube.


Conclusion

With this brief discussion, we wanted to give some information on the causes of malfunctioning of the refrigeration equipment and provide some indications to remedy some problems.

It is obvious that they will be insufficient in many cases but they can indicate the right way to become a "good refrigeration engineer".

Please refer to all the topics covered in the complete section: Refrigeration.

good job

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