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  • Mechanical damages

  • Electrical damages

High discharge temperatures

The most frequent causes that lead to High discharge temperatures:

  • High discharge temperatures

    Compressor overheating and the resulting heating of the oil cause the oil to lose its viscosity. When this happens, the oil cannot suitably lubricate the moving parts. The lack of lubrication causes specific elements, such as the bearings, to excessively overheat and to wear out quickly, and cause the oil to carbonise.

    Among the most common causes are a high value of the compression ratio and a low refrigerant load. These phenomena cause a low flow of refrigerant. Since the heat from the motor and from the friction caused by a compressor are always present, any phenomenon that reduces the flow of refrigerant gas, to a level outside the limits, will lead to the compressor not being cooled enough, causing consequent high discharge temperatures.

    Oil loses viscosity at temperatures between 85º C and 95º C, which causes the protective film to be eliminated and the consequent metal-metal contact, which will cause the compressor to mechanically fail.

    The discharge temperature cannot be higher than 125º C, as it can be damaging to the oil.

    A high compression ratio is generally attributed to problems with the condenser or evaporator, inadequate system control or a combination of all three.
    To rectify the problem, we recommend verifying that the condenser and evaporator are clean, checking the air or water flow and temperature from the condenser and evaporator.

    A low refrigerant load is characterised by the presence of gas bubbles in the liquid line glass sight, due to the low intake pressure and greatly overheated gas.

    To rectify the problem, you must add refrigerant to the system, after first determining why refrigerant is being loss.

Ineffective system lubrication

The most frequent causes that lead to Ineffective system lubrication:

  • Oil dilution

    This is the most common problem, owing to the great affinity it has with the refrigerant.
    The oil may become too diluted owing to the refrigerant during prolonged stop, making it lose part of its lubricating qualities.

    Depending on the type of oil, the oil-refrigerant blend can also become saturated, causing the two fluids to separate. The denser blend, rich in refrigerant, will go to the bottom of the housing, while the less dense and oil-rich blend will remain on the top.
    When a compressor is started up with too much refrigerant in the housing, the refrigerant-rich blend is suctioned by the oil pump. As it is an excellent solvent, the refrigerant removes the oil film on the two bearings.
    Furthermore, highly-diluted oil produces a foam that makes the pump lose its pumping ability. All of this causes serious damage to the bearings, crankshaft and piston-connecting rod set.

    These phenomena happen because the compressor is the last element to cool after a stop and is also the last to heat up as the temperature of the system rises. Therefore, the compressor is the coldest part of the system after several hours of the equipment being turned off. The emigrating refrigerant will gather and condense in the bottom of the compressor, causing the oil to dilute, due to affinity between them.

    To prevent dilution, we advise using a heating element in the compressor housing, as this will reduce the oil-refrigerant affinity and therefore prevent the migration of the compressor liquid. It is important for the resistance is heating the housing oil, primarily during prolonged stops.

  • Loss of oil

    Losing oil is very damaging for the crankshaft and other moving parts, since they cannot sufficiently cool and excessive heat is generated.

    Some of the most common causes for this loss are: too short of cycles, too much oil foaming and long periods with minimum loads, accompanied by incorrect pipe sizes.

    During short-cycle periods, the compressor can pump oil for inside the system at a higher percentage than is being returned. The result is obtaining a reduced level of oil.

    When the oil foams inside of the housing, it will be carried by the refrigerant gas and compressed inside the system. If foaming persists, the oil level may drop. Foaming may be due to oil dilution or due to using unsuitable oil.

Liquid hammering

The most frequent causes that lead to Liquid hammering:

  • Return of refrigerant liquid to the compressor due to an incorrect expansion valve, a damaged evaporator fan or obstructed air filters

    An oversized expansion valve or one that operates poorly –in the case of a failure of evaporator fan (incorrect air distribution in the battery) or obstructed air filters– can cause a return of liquid as a consequence of liquid hammering.
    This will happen when the refrigerant liquid exceeds the evaporator capacity and returns through the compressor intake line, as liquid more than as steam.

    During the operating cycle, liquid flooding the compressor may cause wear to moving parts due to the dilution effect to the oil and the loss of oil in the compressor. During the stop cycle, the migration of refrigerant to the compressor can happen very quickly, giving rise to a liquid hammering when turned on.

  • Migration of refrigerant

    This is the term used to describe the accrual of refrigerant liquid in the coldest part of the system or, in other words, the refrigerant condenses in the coldest part of the system. Generally, this part tends to be the compressor when outside temperatures are too low or when they are too high, although this may also happen in the evaporator.

    Migration occurs mainly when the compressor is at a physically lower level than the evaporator or condenser.
    To prevent the migration of refrigerant liquid coming from the condenser, we advise installing a retention valve on the compressor discharge line. It is also advisable to install a U-bend at the condenser inlet.

    With respect to evaporators, we advise stopping the compressor for liquid collection. We also recommend installing a U-bend right at the outlet of the evaporator.

    Without these precautions, it is very likely that large quantities of refrigerant liquid return through the compressor’s intake or discharge line, causing a liquid hammering and the dilution of the oil.

    We advise have a heating element in the compressor housing. Although it does not guarantee avoiding this phenomenon, as depending upon the quantity of refrigerant, the capacity of the heating element may be surpassed.

  • Oil return

    The return of oil is just as damaging as the return of refrigerant liquid. It normally happens when the pipes are not properly designed and, as a consequence, there will not be uniform movement of the oil throughout the installation, causing an accrual of oil hammering.

    This excess oil leads to a significant reduction in the system’s cooling ability, as the heat exchange capacity in the evaporator is drastically reduced.

    Take special precaution for systems with more than one compressor in parallel or in tandem.

Return of liquid

The most frequent causes that lead to Return of liquid:

  • Return of liquid

    The return of liquid is mainly caused when the gas overheats in the compressor intake moves towards 0 K, owing to the detergent effect of the refrigerant, which can remove all the lubrication film from the compressor’s moving parts. This phenomenon will cause these parts to break.

    When the compressor undergoes a return of liquid, we can see how the parts of the compressor end up clean, namely, without any trace of oil and no signs of carbonisation.

System contamination

The most frequent causes that lead to System contamination:

  • Rust

    It frequently appears in maintenance operations such as oil changes. Oil has oxidising characteristics that, with the combination of oil and water, can cause oxidation and rust.

    Rust also forms in pipes when heat is applied during welding in the presence of air. This can be prevented by decompressing the air inside the pipe with inert gas, such as dry nitrogen, before applying heat.

    Rusting can be removed by installing an intake filter before the compressor, which will retain these elements, thus preventing their entry into the compressor. After start up, we advise changing this filter again.

  • Copper plating

    This happens in 2 phases:

    In the first, the copper dissolves in the by-products from an oil-refrigerant reaction. The quantity of copper dissolved is determined by the nature of the oil, by the temperature and by the presence of impurities. In the second phase, the dissolved copper is deposited into the metal parts in an electro-chemical reaction.

    High temperatures are the factor that most heightens this problem. A second factor in the formation of copper coating is the use of improper oil. Specific oils react more easily with refrigerants than others, under the effect of high temperatures, causing the copper to dissolve.
    Finally, the presence of air or humidity and other contaminants accelerate the movement of copper into the parts such as the valve plates, oil pump and crankshaft.

    To prevent these types of problems, we advise always using the type of oil recommended by the manufacturer, analysing and correcting the causes of high temperatures and evacuating the system as many times as necessary to ensure that all air and humidity are removed. We also advise using a filter drier with a high moisture absorption power.

  • Humidity


    The presence of humidity in the system, whether in air or water, can lead to other contamination owing to the formation of oxidation, rust and decomposition of the refrigerant.
    Excessive heat from friction, copper coating and worn-out surfaces can be related to this contaminant.

    The main source of contamination from humidity is the air that enters the system when the pipes are being installed. Another way that humidity may enter is through unsuitably handled and used oils as replacements for the original compressor oil.

    Without suitable evacuation and dehydration methods for the refrigerant system, a small quantity of water or air can induce rust and accelerate the process of the formation of other types of contamination.

    Humidity can be detected by analysing the oil or using a liquid sight glass in the liquid line.
    The safest way to remove humidity is to conduct a good evacuation, followed by a vacuum breaker. We recommend doing this process a couple times using dry nitrogen.

  • Dirtiness

    Foreign materials, such as dirt, welding flux and chemical products, in combination with the air, cause chemical imbalances that cause the oil molecules to break. Along with high system discharge and friction temperatures, this can result in the formation of acids, sludge or a combination of both.

Burnout located

The most frequent causes that lead to Burnout located:

  • Burnout located

    When there is a mechanical breakage, some of the metal parts may be housed in the winding mechanisms, causing damages to the insulation of the motor. This loss of insulation can cause a short circuit between the poles. The heat from this short circuit can burn out the insulation in the surrounding poles, which can end up causing a phase or a phase-earth short circuit.

    A burn at a specific point can also be caused by strain to the motor.

Complete burn

The most frequent causes that lead to Complete burn:

  • Complete burn

    Occurs, for example, when one of the phases is out of phase.
    When the motor is stopped is when there are greater chances that the motor will burn out completely. This is because when it is energised, electric and physical demands on the coils are greater. If the voltage is low or the compressor is mechanically blocked at this moment, the compressor will burn out if the motor protector does not act in a very short period of time.

    Another of the most common causes is inadequate cooling of the motor due to a low flow of intake gases.

    In short cycles, the motor can also overheat. Frequent powering up, with the consequent current peaks, and a reduced flow of intake gases cause the motor to overheat, which can end up burning out the motor.
    To prevent this from happening, we recommend that you install some type of timing device to limit how often the compressor powers up.

Electric failures caused by mechanical problems

The most frequent causes that lead to Electric failures caused by mechanical problems:

  • Electric failures caused by mechanical problems

    Motor overrun is one of the most common causes when there are mechanical problems in the compressor.

    Wear to bearings can lead to a runout between the rotor and stator. Because the space between them is very small, this runout makes the rotor damage the stator laminations, causing a failure in the slot insulation, which will in turn cause a phase-earth short circuit.

    Worn-out bearings are the main cause of motor overrun. This can occur due to dilution of oil or by some type of contamination of the oil.

    Oil that contains suspended particles can reach the motor through the intake pipes, causing damage to them.

Lack of phases

The most frequent causes that lead to Lack of phases:

  • Lack of phase

    In a three-phase motor, a lack of current can cause it to perform like a single-phase motor. This means that the other 2 phases work with too much current. If there is no protector to turn off the motor, the 2 phases will burn out quickly.

    Or one of the phases could overheat before the other one, so that one of them does not burn out.

Wiring done wrong

The most frequent causes that lead to Wiring done wrong:

  • Wiring errors (single phase motors)

    Wiring errors in single-phase motors are quite common. This happens by connecting the auxiliary phase as the main one or incorrectly connecting the electric components.

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SIFA is the exhibition dedicated to Refrigeration and its Application, which will take place in Lyon France, on 28-29 November 2018 AREA Innovation & Commitment
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Dear Customer, We need to inform you that Bristol Compressors will close their factory within maximum 2 months.

Large business losses in Middle East is the most significant contributor for this decision. Beside this unpleasant news, our role is to bring you all the support you need to make a smooth transition from Bristol.

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