maintenance of central air conditioner

Figure 1: Maintenance staff works on an exterior unit of a central air conditioner.

1. Reasons of High Temperature Breakdown

1.1 Environmental Factors

Ambient temperature may not be the main cause of high temperature shutdown, but it is often the inducement of compressor high temperature shutdown.

Generally, technicians have a design operating environment temperature (30-40 ℃) when designing compressors. When the air compressor is operated under the designed operating environment temperature, its maximum temperature is close to the protection temperature of the air compressor.

If the ambient temperature of the air compressor is higher than the designed operating ambient temperature, the temperature of the air compressor will be increased, so that the air compressor will reach the shutdown temperature or even exceed the shutdown temperature of the air compressor, resulting in high temperature damage of the compressor.

Danfoss Compressor HM-GMG064-FL

Figure 2: Danfoss Compressor HM-GMG064-FL

1.2 Mechanical Malfunction

Oil Cut-Off Valve

If the oil cut-off valve (also known as oil stop) works abnormally, it will lead to the rapid heating of the main engine due to lack of oil. In serious cases, the screw of screw air compressor will be burned.

Oil Filter

The breakdown of the oil filter will not only affect the supply of compressor oil, lead to insufficient lubrication of the equipment and cause high temperature, but also hinder the normal circulation of compressor oil, and affect the heat dissipation of the compressor, and cause temperature rise of the compressor.

Thermal Control Valve (Temperature Control Valve)

The thermal control valve is installed in front of the oil cooler, and its function is to maintain the exhaust temperature of the machine head above the pressure dew point. If the thermal control valve fails, the lubricating oil may directly enter the machine head without passing through the cooler, so that the oil temperature cannot drop, which will resulting in overheating in the end.

Oil Regulator

The function of the oil regulator is to control the oil injection quantity of the compressor. If the oil injection quantity is insufficient, the compressor will be at high temperature.

In this case, the oil injection quantity should be increased appropriately. However, maintenance personnel should pay attention that the oil regulator has been calibrated when the equipment leaves the factory, so it is not recommended to use the enterprise to adjust it privately.

If you are the maintenance staff, you should negotiate with the equipment manufacturer or ask for help of professionals for the equipment.

Oil Cooler

Abnormal compressor oil cooler is common in water-cooled air compressor. Check the temperature difference between the inlet and outlet of the cooler. If the temperature difference is less than 5 ℃, the heat exchange effect of the cooler will be greatly reduced. The reason of this failure is that the cooler is blocked or scaling. At this time, the cooler can be removed for cleaning. For air-cooled air compressor, more attention should be paid to whether the ambient temperature is too high and whether the cooling fan works abnormally.

Copeland Compressor ZP103KCE-TFD-250

Figure 3: Copeland Compressor ZP103KCE-TFD-250

Compressor Head

The abnormal wear of air compressor head causes the increase of heat production and high temperature. There are two common reasons for this fault: one is the poor lubrication of the air compressor oil, the other is the cause of the head itself. The solution is to replace the qualified air compressor oil, or replace the air compressor head.

Air Filter

The air filter is blocked and the gas production is too small, which causes the load of the air compressor to increase. With the increase of air compressor load, the air compressor will be in the loading state for a long time, resulting in the increase of heat production and high temperature.

In this case, you should replace the air filter.

Oil-Gas Separator

The blockage of the oil-gas separator causes the internal pressure of the air compressor to be too high, resulting in high temperature.

There are two reasons for this failure: first, there are problems in the quality or service life of the oil-gas separator itself; Second, the quality of the air compressor oil is not up to standard, and its poor separation ability from air causes the blockage of the oil-gas separator. At this time, the oil-gas separator or air compressor oil should be replaced.

Sensor and Computer with Incorrect Reading

If the temperature sensor fails, it will cause the PLC to send a false report of high temperature, which can lead to the shutdown of compressor.

Danfoss Compressor MLM019T5LP9 380-415V 3PH 50HZ 460V 3PH 60HZ

Figure 4: Danfoss Compressor MLM019T5LP9

1.3 Factors of Compressor Oil

maintenance staff adds oil to screw compressor equipment

Figure 5: A technician adds oil to compressor equipment.

Insufficient Oil

During the operation of the air compressor, if the oil level of the air compressor oil is lower than the low oil level mark L or mix, it means that the oil level of the air compressor is insufficient.

The insufficient oil quantity of the air compressor makes the heat dissipation worse, which causes the high temperature of the compressor. At this time, it is necessary to stop and refuel immediately.

Oil Deterioration

Compressor oil due to its own quality problems or over the use of time and oxidation deterioration, resulting in poor oil liquidity, heat exchange capacity decline, resulting in air compressor head heat can not be completely and timely taken away. Stop and change the oil immediately.

Improper Selection of Oil Viscosity

Air compressor oil viscosity is too low, poor lubrication, resulting in abnormal wear of equipment, too much heat, too high viscosity, poor oil fluidity, making heat can not be sent out in time, which will cause high temperature of air compressor. Therefore, when maintaining the compressor, the user should refer to the service manual of the compressor and the actual working conditions of the user to select the appropriate viscosity level.

Nonstandard Compressor Oil

The problems of nonstandard compressor oil are explained as below.

The thermal oxidation performance of air compressor oil is poor, resulting in the deposition of oil sludge and paint film, which affects the fluidity of the oil and reduces the lubricating performance of the oil;

The viscosity temperature performance of air compressor oil is poor, the low temperature fluidity is not enough, and the high temperature lubricity is poor;

The air separation ability of air compressor oil is poor, which affects the oil-gas separation.

So up till now, we have talked about common reasons for high temperature faults of screw air compressor.

For users, how to avoid or find the compressor problems in time, so as to reduce possible loss of production accidents and costs?

Danfoss Compressor MTZ56-4VM

Figure 6: Danfoss Compressor MTZ56-4VM

2. Solutions for High Temperature Problems of Screw Compressor

2.1 Choose Suitable Environment and Equipment

Setting of Compressor Station

When installing air compressor station, users need to design the location of air compressor, air storage tank, desiccant, filter and other common equipment in advance.

As users and maintenance personnel of the compressor, you should also consider that sufficient heat dissipation space and maintenance space should be reserved between equipment and equipment as well as between equipment and wall.

The air compressor station should be kept under good ventilation and with a least an exhaust fan installed when necessary. If the air compressor station is built outdoors, it is necessary to do a good job in dustproof, waterproof, antifreeze, explosion-proof and drying treatment to avoid damage to the air compressor due to dust, moisture and extreme high and low temperature.

In addition, it is better to reserve an area for the maintenance of the air compressor in the air compressor station, and the area required for the maintenance of the largest air compressor in the air compressor station shall prevail, so as to ensure timely and convenient maintenance in case of air compressor failure.

Regular Maintenance of Compressor

Users should form a good habit of regular inspection and maintenance, and insist on writing maintenance and repair records.

The inspection scope includes the leakage of grease for compressed air and air compressor, regular replacement of lubricating grease and other vulnerable parts as required, regular detection of voltage and current of air compressor station, surface cleaning and environmental cleaning of air compressor and other equipment, etc. Detailed inspection and maintenance can refer to the equipment maintenance manual.

2.2 Select Qualified Accessories

accessories of air compressors, seal packing, temperature sensor, nozzles, air filter, and wires

Figure 7: Accessories of air compressors.

Users choose suitable accessories, including air filter, oil-water separator and other common vulnerable parts, as well as air compressor oil for lubrication.

As for the selection of air compressor oil, the following suggestions are given:

Use Compressor Oil of Appropriate Viscosity

You should evaluate the quality of compressor oil based on both its lubricity and fluidity.

If there is no special requirement for the working condition of air compressor, the user can select it according to the equipment manual.

If the working condition of the air compressor is special, it needs to be adjusted according to the actual working condition.

For example, if the working temperature of air compressor station is high, the influence of temperature on viscosity should be considered, and the viscosity can be increased appropriately; If the air compressor station is outdoors and the temperature difference between day and night is large, it is necessary to choose the air compressor oil with better viscosity temperature performance.

Use Compressor Oil with Good Thermal Oxidation Stability

For air compressor, because of compressed gas, 20% oxygen content is a big problem for the antioxidant performance of compressor oil. Thermal oxidation stability can not only prolong the service life of compressor oil, but also reduce the deposition and accumulation of sludge, paint film and other substances caused by high temperature oxidation.

These are very important factors that cause high temperature of compressor and affect normal operation of compressor. In addition, the acid produced by oxidation also has adverse effects on the metal parts in the compressor to a certain extent.

Use Compressor Oil With Good Air Separation Performance

The control of air release and foam will not only affect the lubricity of the compressor, but also affect the separation effect of the compressor, and to a certain extent, it will also affect the service life of the oil separator.

In addition, if the effect of oil-gas separation is not good, the oil content in compressed air will be too high, which will affect the subsequent production and product quality.

Use Waterproof Compressor Oil

Especially in the coastal area, outdoor air compressor station and other air humidity is large, the moisture content in the air is high, the existence of condensate is easy to cause the emulsification of compressor oil, thus affecting the performance of compressor oil, so users need to choose the compressor oil with good water resistance.

Track and Record Oil Status Regularly

If conditions permit, regular oil detection is necessary for users. Through regular sampling, the performance change of compressor oil can be detected.

By observing the performance changes, you can find many potential problems and faults of compressor in time. At the same time, accurate oil change guidance are helpful for users to avoid oil waste.

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