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Air Conditioning Refrigeration System Failure

Use a pressure gauge to check the fault of the air conditioner refrigeration system of the excavator. Generally, the compressor is stopped and operated. After the compressor has stopped running for more than 10h, the high and low pressure of the compressor should be the same value. If the values indicated by the high and low pressure are not equal, it indicates that there is blockage inside the system, and the expansion valve, the liquid storage bottle and the pipeline part should be inspected.
When the compressor is in operation, the engine speed is controlled at 1500-2000r/min, and the air conditioner is started to operate the compressor. Under normal circumstances, the pressure on the low pressure side is about 150-250 kPa, and the pressure on the high pressure side is about 1400-1600 kPa. If the pressure indication does not match the normal value, the fault diagnosis can be performed as follows.

The indication of the high and low voltage meter is lower than the normal value at the same time
This may be due to insufficient refrigerant. When inspecting, it can be found that the high-pressure tube is slightly hot, and the low-pressure tube is slightly cold, but the temperature difference is not large. It can be observed from the sight glass that bubbles appear every 1-2s. At this time, check for leaks and make up the refrigerant after filling the leak.
Low pressure gauge is much lower than normal
At this time, the fuzzy mist flow can be seen in the sight glass, and there is no temperature difference between high and low pressure, and the cold air is not cold, indicating that the refrigerant is seriously leaked.
The low pressure gauge indicates near zero and the high pressure gauge indicates a lower than normal
At this time, the air conditioning system often shows that the air is not cold, and the pipelines before and after the expansion valve are frosted. The reason may be that the expansion valve is blocked by frost, so that the refrigerant can not be circulated in the system. At this time, the vacuum should be repeatedly applied to re-add the refrigerant; on the other hand, the expansion valve may be damaged by the temperature sensor, resulting in the expansion valve not being Turn on, you should check the temperature package at this time.
High and low pressure gauge indications are too low
This could be an internal fault in the compressor, such as a valve plate pad, a broken valve plate, and a need to replace the compressor.
High and low pressure meters are higher than normal
The surface temperature of the suction pipe of the compressor is lower than normal, and it is wet and cold (commonly known as sweating). Due to the excessive opening of the expansion valve, the refrigerant in the evaporator is “oversupply”, which affects evaporation and reduces the corresponding heat absorption. , resulting in insufficient air conditioning cooling. At this time, if the opening degree of the expansion valve can be adjusted, the opening degree should be reduced; if it is not adjustable, the expansion valve is replaced.
High pressure and low pressure on both sides are too high
This indicates that there are too many refrigerants, and the two hands touch the compressor into and out of the gas pipe, and the high pressure side has a hot hand feeling, the low pressure side can see the frost, the air conditioning system compressor turns off the power supply and stops running, and the rest continues to work, after more than 45s, The mirror is still clear and free of bubbles, and it can be concluded that there is too much refrigerant and excess refrigerant should be discharged.

Low pressure gauge indication is too high, high pressure gauge indication is slightly higher
This may be due to insufficient cooling of the condenser. If the condenser is cooled with cold water and the pressure of the gauge becomes normal, it can be concluded that the condenser is insufficiently cooled. If there is such a failure, the cooling effect is good when the air conditioner is just turned on, the working time is long, and the cooling effect is poor. If the heat sink of the condenser is clogged, the engine water temperature is too high, and the condenser air volume is insufficient, there may be a problem with the fan or fan belt.
Low pressure gauge indicates zero or negative pressure, high pressure gauge indicates normal or high
Cold air is sometimes cold and sometimes normal. This phenomenon indicates that there is moisture in the refrigeration system or the moisture absorption capacity of the dryer is saturated. The water enters the refrigeration cycle system, freezes at the small hole of the expansion valve, and returns to the normal state after melting. At this time, the dryness should be replaced. Bottle or repeatedly vacuum to remove moisture from the system.
Low pressure gauge indication is low, high pressure gauge indication is too high
This phenomenon is generally caused by blockage of the refrigeration system. Blockage often occurs at a position where the passage section of the refrigeration system is small. Most of the components that are prone to blockage are on the high pressure side of the refrigeration system, such as a dry filter, an expansion valve screen, etc., and are blocked. The phenomenon is generally caused by moisture, dust, and the like contained in the refrigerant, and the clogging portion often has frost formation. After finding the blocked part, remove the blocked parts for cleaning or replacement. If the blockage is serious, the refrigeration system should be completely disassembled and cleaned in sections.
The low pressure gauge is too high and the pressure of the high pressure gauge is too low
This phenomenon often indicates a leak inside the compressor and the compressor should be replaced or repaired.
The low pressure gauge is slightly higher and the high pressure gauge is slightly lower
No air-conditioning, there is condensation or a layer of frost on the suction pipe of the compressor. It may be that the expansion valve is damaged. It is necessary to replace the expansion valve and charge the refrigerant.

Air Conditioning System Fault Repair

First, fault analysis and diagnosis:
Before the fault is checked, the vehicle should be parked in a cool place with good ventilation, away from fire and wide terrain. The analysis and diagnosis of faults is generally carried out by combining the visual method of visual inspection, ear hearing and hand feeling with the measurement method of instrument test.

  1. Intuitive method: It is to judge whether there is a fault by intuitive feeling.
    (1) Visual inspection:
    1 Check if the wear of the engine drive belt is serious.
    2 Check if the compressor pulley is positive and the compressor is installed firmly.
    8 Check the condenser fins, it should be neat and tidy, clean and free of blockage.
    4 Check the evaporator, it should be clean, free of obstacles, well ventilated, if necessary, should be cleaned.
    5 Carefully check the refrigerant piping and fittings. It should be clean and free of oil. If there is oil, there may be a leak here.
    6 Check the system piping for scratches, bending pleats, flattening or breaking, and if so, exclude them.
    7 Check whether the connection of the hot water supply pipeline is reliable, and whether the hot water valve is opened and closed freely.
    8 After the machine has been running for a period of time, there is no frost or ice on the external parts.
    9 Observe the flow state of the refrigerant from the sight glass: first start the engine, stabilize it at a certain speed for two minutes, and observe the flow state of the refrigerant from the sight glass. If it is clear, and there is no cold air blowing, it means that the refrigerant has leaked light; if there are bubbles, it means that the refrigerant is insufficient or the refrigerant contains air and moisture, and the refrigerant is insufficient. It can be distinguished by adding refrigerant, such as bubbles. If it is eliminated, it means that the refrigeration pipeline contains air and moisture. The refrigerant should be discharged, and vacuuming, pressure keeping and refrigerant injection should be carried out. If there is oil grain, the refrigerant has leaked light. If there is dirt, the system has been polluted. Need to be cleaned.
    (2) Ear listening: The ear is listening to whether the sound in the fan, compressor and air conditioning system is normal.
    (3) Hand feeling: It is to check the tightness of the belt by hand, and it is required to be elastic. It is possible to press the middle position of the belt with a force of 98 N, so that the pressure can be 7 to 10 ram. In addition, there should be no difference in the temperature at which the liquid storage dryer enters and exits the pipe.
  2. Instrument measurement method: mainly through the manifold pressure gauge, thermometer, multimeter, leak detector, etc. for testing and inspection. (1) Check with manifold pressure gauge: Connect the manifold pressure gauge to the high and low pressure detection interface of the compressor. Under the static and running state of the compressor, the fault can be found according to the reading of the meter. When the ambient temperature is 30 ~ 35 ° C, the compressor speed is 1800 ~ 2000r / min, the cold air switch is at the strongest speed, the maximum speed of the fan, the pressure of the low pressure valve is 0.13 ~ 0.20MPa, the pressure of the high pressure valve is 1.47 ~ 1.67 MPa, indicating that the refrigeration system is normal.
    (2) Check with temperature meter: When the air conditioner works normally, the temperature of the condenser inlet pipe is about 70 °C, the temperature of the condenser outlet pipe is about 50 °C; the liquid storage tank is about 50 °C under normal conditions; the evaporator is at Under the premise of no frost, the outlet temperature is usually around 10 to 14 °C.
    (3) Check with the leak detector: Check the leak of the air conditioning system through the leak detector.
    (4) Check with a multimeter: Use a multimeter to check whether the system circuit is normally on and off, whether the contact is good, and whether the electrical components are working properly.

Second, system components common faults

  1. Compressor:
    (1) Leakage of compressor leakage includes leakage at the shaft seal, leakage at the inlet and outlet, leakage at the cylinder head, leakage at the oil filler, cracking of the cylinder block, and leakage caused by poor sealing of the O-ring of the front casing.
    (2) Abnormal noise The abnormal noise may be caused by improper air gap adjustment, insufficient refrigerant, deflation valve spring or intake valve spring rupture, clutch slippage, etc.
  2. Clutch:
    (1) With a non-moving compressor, the overloaded meshing surface is slipped, overheated and ablated.
    (2) The fixed coil and the rotating part rub, causing the electromagnetic coil to be damaged. The resistance of the electromagnetic coil is a few ohms. If it is too large or too small, it means abnormal.
    (3) The clutch clearance is incorrect, and the clearance value is generally 0.45 to 0.75 mm.
  3. Condenser and evaporator:
    (1) Common faults are caused by vibrations, etc., and repair welding should be performed.
    (2) The surface is dirty, so that the heat dissipation performance is deteriorated. Brush and water are used for cleaning, but do not use high-pressure water to clean, so as to avoid deformation and distortion of the heat sink and affect heat conduction.
  4. Liquid storage tank:
    (1) The filter tank desiccant filter is damaged and the desiccant is leaked.
    (2) When the temperature and pressure of the system desiccant are too high, the melt plug is easily melted, causing the refrigerant to leak.
  5. Expansion valve: The most common fault of the expansion valve is blockage, which causes the blockage. First, the system is not clean enough. Second, there is moisture in the system. If the inside of the system is contaminated, the system should be cleaned in time; if the water in the system is large, the dryer should be removed and the desiccant replaced.
    1. High and low voltage switch: When the high and low voltage switch is working normally, it is connected. The main fault is that when the system has high voltage or low voltage, the switch will not be disconnected. It should be removed and checked. If it does not meet the requirements, it should be replaced.
      three. Common faults and causes of the system
      Common faults in air conditioning systems can generally be divided into: electrical faults, mechanical faults, faults caused by refrigerants and refrigeration oils. The concentrated performance of these faults is: the system does not cool, the cooling effect is not good, or abnormal noise occurs.

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